My 2011 iMac was booting slowly and needed more disk space. I figured a new SSD would help it to run faster so I could reliably use it for music recording / production again.
Everything went fine! I was scared to take the screen off but it turned out to be much easier than I expected. As long as you sort all the screws you take out of the computer, and keep them from getting lost, reassembly will be a breeze. Overall it took me maybe two hours from when I started to my first boot with the SSD installed.
I'm still not sure whether I went about installing OS X on my SSD in the best way - transferring all my applications, and especially my music plug-ins, to the new boot drive has been much harder than actually installing it was!