Wanted to gift my 2007 iMac 24" to my father in law. His Mac iBook (also a gift from us) recently died. The years were starting on show on this 5 year old machine, particularly with the latest OS X.
Thanks to iFixIt I swapped the magnetic HDD for a SSD. I also upgraded the 2GB of RAM to 5GB. These two upgrades breathed a few more years of speedy usage into the iMac, even with the latest and greatest Mountain Lion.
By the book
$150 in upgrade parts made a great gift. Reuse beats recycling.