On the iMac there is some thermal sensor that connects to the hard drive and makes this a bit tricky since non-Apple SSDs don't have that feature. Is this true for the 2011 MacBook Pros?
I replaced the stock 500GB 5400rpm hard drive in my Early 2011 Mac Book Pro (MacBook Pro 8,2) with a 120GB OWC Mercury Electra 6G SSD a few weeks ago. There was no thermal sensor attached to the stock drive. So far the replacement has worked fine, no issues at all.
Hardware Monitor application reports the temperature of the SSD, so the computer must be properly polling the internal temp sensor in the drive (over the SATA interface,) and/or there may be a permanent sensor attached near the drive on the inside of the MacBook Pro's case. (But not actually attached to the drive.)
Screen capture of output from Hardware Monitor:
There was no difference in the software install process (vs. a regular hard drive.) In fact, I used 2 external cases (and a 3rd, separate, bootable drive) to do a block copy from the original 500GB to the new 120GB SSD. No issues.
About TRIM support: The drive itself is capable of it (See "TRIM Support" at the bottom of the specs page for this drive.), however, Mac OS X 10.8.2 does not support TRIM for this drive, at this time. The drive vendor OWC says you don't need TRIM anyway because SandForce's firmware makes it unnecessary or even counterproductive. I agree with their explanation.
Screen cap from my System Profiler:
As another data point on SSDs -- I had a 60GB OWC Mercury 3G SSD in a 2009 Mac Mini for about 3 years, never had any problems with it whatsoever.
2013-04-30 UPDATE -- I had some firmware problems with the new 120 GB OWC Mercury 6G drive. The drive would not be recognized at system startup time without doing multiple (10 or more) PRAM & SMC resets. Finally it would "catch on" & then start up and run fine for weeks. Eventually it stopped responding altogether. (OWC had suggested that I apply a firmware update, but I wasn't able to do this because I don't have a working DVD reader / writer.)
I am returning the drive to OWC for a warranty replacement. It always pays to BACK UP YOUR DATA every single day, or even several times a day.
As long as you have the correct screwdriver(s) for internal access you can replace the HDD with an SSD.
I apologize for not catching the full question.
Folks at iFixit did a teardown of the 15" and there is no thermal sensor attached the HDD.