I am really happy with my Mac Mini - model 2011, but wanted to speed things up a bit. Already upgraded the Mac with more memory. I ordered the Dual Hard Drive Kit from iFixit earlier this year and already had a SSD (500 Gb Samsung 840). I want to boot from the SSD and use the original HDD as an extra data disk for photo's, downloaded stuff and so on. And now finally had time to upgrade my Mac Mini.
Quite easy. First I made sure to have Time Machine make the final backup. Then with the excellent guide I was able to assemble the kit and SDD and put the Mac Mini back together. In the meantime cleaned the fan and the inside of the Mac Mini of any dust. After that booted up the Mac Mini from an earlier prepared OS X Mavericks USB drive, installed OS X and restored all settings from the Time Machine. After checking all the settings and files reformatted the original HDD.
It took about 45 minutes for me to install the SSD including reading the guide. Installing OS X was 10-15 minutes, restoring from Time Machine backup took about 1,5 hours. No issues or glitches at all. Great!
The Mac Mini is way faster now!
My advice is that this kit is worth the investment, the machine feels like a new one due to it's booting time and smooth running programs.
My other advice is to read and follow the guide and take your time. The guide is great, photo's are clear and the guide is precise. And again, take your time, anyone can do this!