I just got my iMac back with ML installed, I will keep anyone interested here posted on how it compares with Lion and Mavericks.

When I bought my big iMac (27 inch 3.4ghz) it developed a rather obnoxious blue line down the centre of the screen. I took a pic with my phone and then took it into the shop where I bought it .. they replaced the whole screen. Apparently this had been a known problem with the iMacs but apple will replace it without any arguement.

Ever since then that computer has been great. It's a mid 2011 model .. and I own three of them. One was a swap for my 17inch MacBook Pro which i toasted, and the other was ex-demo from my local drug store so I got another 27 inch iMac about $500 cheaper than it should have been :D

Anyways, as I say, apple are usually pretty good about replacing bum parts. As for Mavericks .. I like it, I can't say I see any huge performance boost over previous OS's but that may be because I've used it for a while so I've gotten used to it. I do appreciate it's networking and in order to maintain a good connection between my Mac's I upgraded all my machines to Mavericks. Also it gave my the excuse to dump Logic 9, and Pro-Tools 10.

High end iMacs are actually surprisingly powerful computers .. I can't say they'd be as powerful as a previous gen. Mac Pro but I'd bet they'd give 'em a run for their money. I'm still waiting for delivery of my brand new shiny Mac Pro (3.5ghz 6-core). But here's a nice thing I found out .. using the thunderbolt connection you can use the 27inch iMac as a display for the Mac Pro, and it works as fast and well as plugging it into a standalone 27inch cinema display .. so that's pretty cool. So I already have 2 x 27 inch screens for my Mac Pro to use. That's very nice as it saves me spending another $1,000 on screens for it.

Jusr wish it would hurry up and get here!!! ::taps foot::

When I installed Mavericks my computer's speed went down on a parabolic slump in terms of speed, and I am not talking professional applications, I am talking opening Safari, lag in responding when clicking on an Apple menu item, changing from account to account, etc., without me having done anything else. I read in several fora that this could be the case because of a program that might conflict with the OS and other CRAP. I have been working with Macs since 1988 and this is the very first OS - and without shifting the paradigm, i.e. not going from 9.2 to X - is so "sensitive" to the user's hard drive's contents.

1) Apple should have stipulated that users empty and re-format their computer before installing due to the real danger that Mavericks could turn it into jelly.

2) They should rescind their cretinous and so greedy recent practice of not including the OS CD in the packaging of a $2,500 computer, since in the event of upgrading to a different OS it is a real inconvenience to revert to the older one.

I installed Mountain Lion recently after re-formatting the computer, I will give my thoughts once I get some experience in working with it, already it seems slower than Lion.

Why dont you do what I have proposed :

 Make one partition with Maverick and another with ML

Install Logic on both partitions

Dont forget to update all software

and do comparaision

From what I have read Logic is said to be working faster with Mavericks

I have gave you the link to make your CD

Cyril thank you for monitoring this and sending me the link last week or so. However, I took my iMac at the shop so I could have my faulty graphics card replaced, so I asked them to also install Mountain Lion on my computer. I got it back and erased my hard drive completely so that I could erase the dummy account they had created, and start fresh. Only to my astonishment my computer cannot find my hard drive anymore, it can only see the partition with the operating system on it. I found out yet another reason why Jobs was a one-man-show genius:

Those universal twirps at Apple won't let me install ML again from the Internet because they can't associate my computer with either a Lion or ML in the App store (although I registered my computer promptly when I got it with Lion on it). And my question is: How ******* hard is it to include an OS DVD in the package, and why oh why does the system itself ERASE the installer automatically after the installation??!! Which is why I cannot use your wonderful link, for which I have to have the installer in order to create the bootable DVD. I presume the whole OS 10.8.5 is still intact in my OS partition which I can still see on my system. I just have no access to it. So Monday will be yet another wasted day of my driving down to the authorized service, screaming!

If you erase a HD it is normal you loose everyting !

If you had create a partition instead you will not be in that s...

In the good old days, when we erased/re-formatted the HD, we had a DVD from which to re-install the OS. To my understanding, this great practice was replaced recently by a separate (to the HD) partition inside the computer, in which the OS resides in case one has to re-format the HD. That partition is still there in my computer (with 10.8.5 on it), I can still access it, but it does not re-install my ML OS on its own. It asks for an Internet connection to the App store - another Mac-genius idea..... - and when I connect to that I am told that it doesn't show I have ever bought Lion! Which is true, I never bought Lion, I bought an expensive computer with Lion on it, which I did register immediately with those geniuses!

The only reason that I erased my HD in the first place is that some people in fora suggested that, yes, Mavericks is merde, but it seems to be running faster with a clean install (which wasn't the case with me). And I tell you, this situation is going to be resolved for me somehow, mostly since I did buy this computer with Lion on it and the App store's records are wrong. The question remains why do I have to go through all this, instead of them just providing a DVD in the original package, or allowing you to re-install from that separate stupid partition, without having to connect to the Internet. Not everybody wishes to live in their stupid Cloud...

You can buy it and ask after for a refund

Erik go to the Apple Store and I think you can buy Mountain Lion for about £14. 

I agree with you Erik. Apple has turned itself into a fucking shambles. 

The fact that Mavericks may or may not be better than ML according to different pople is neither here nor there. You should be able to access what you want, when you want, with ease and not be dictated to by anyone when you're the one that's paying.

Thanks guys, I'll wait until Monday so that the Apple service shop here is open, and I'll see what happens then. Enjoy your weekend.