Here's some more info on upgrading an 27" Imac with an SSD - the iFixit guide is pretty good but there's some things it doesn't tell you, I'll try to fill in those gaps - hopefully this will help you avoid my mistakes and should make the process quite easy.
- Preparations: SuperDuper is an easy way to backup your entire OS to an external drive (needs to be completely empty) and then restore it afterwards again to the SSD, this can take a considerable time though so better do it beforehand - backing and restoring took about 2 hours each way for 145gb of data for me (backup drive was a slow old 160gb 2.5" usb drive though)
- Lifting the glass cover is pretty easy. some cheap 3$ suction cups easily do the job and the cover is pretty light.
- Removing the sync cable with a pair of tweezers is a bit fidly, so either have a good pair of long tweezers ready or do it by hand - the display can be lifted enough to reach in.
- The sync connector only has contacts on the bottom side so it's easy to remeber which way to put it in again.
- For removing the 8 screws that hold in the screen you need a long narrow screwdriver, my T10 was part of a multitool (where you only replace the very tip) and was too wide to reach in, luckily I was able to remove the screws easily with normal type T9 screwdriver (part of a different set) that I had.
- None of the other connectors needs to be removed if you're only replacing the HD - I used a pair of paperbacks to prop the screen up, and that worked pretty well.
- First remove the sata connectors before unscrewing the HD - they sit pretty tight and if you try to do it the other way around (as I did) the HD will move around and might damage something.
- Take care when buying the 3.5" to 2.5" adapter...I had two on hand, none of which was really suitable (manage to use one, but it was a bit of a hassle...) The main point here is that the adapter needs to have holes for the same type of screws that go into 3.5" HD's...both of mine had slightly smaller ones. The spacing should also be the same as the two outermost holes on a 3.5" HD (on both of mine they were spaced more closely so I was only able to fasten one screw on each side)
The adapter also shouldn't extend too far away from the holes or it won't fit (the akasa adapter I had wouldn't fit in at all).
- An easy way to short the Temp sensor is to use a short bit of a paperclip (I used 32mm ones), just break a bit off bend it around and insert it. Inserting that is easy and it'll sit tight, just wrap some electrical tape around it and job done.
- I think disconnecting the fan as somebody mentioned might be potentially harmful - according to istatmenu that fan still runs at 1100rpm with the wire shorted, so if you disconnect the fan you'll also remove any airflow from that part of the case. The fan running at 1100rpm should be enough to cool what little heat the ssd produces as well as any other parts in that airflow path.
- When screwing the screen back in be very careful with the screws, especially at the bottom end if one slips and enters the case it's a huge hassle to get it back out again...either use a heavily magnetic screwdriver or assist with tweezers. The top end is a bit of a hassle due to the strong magnets there, well at least there's little chance with those screws disapearing into the case ;-)
As for the SSD used:
I originally planned to go with an Intel (already used a 80gb one in my macbook since the end of last year) but with about 145gb of data that I actually want to have on my primary drive that seemed a bit tight - so I went with a 240gb Mushkin Callisto Deluxe instead ( 270mb/s r/w and up to 50000 iops) so far I'm very happy - AJA reports r/w speeds around 260mb/s and that's on a decently loaded drive (145gb of data across 600'000 files)