I was wondering whether I should trash my old iMac from late 2009. Then I decided to try to move it to Linux and upgrade a little bit, so I bought these 16 GB (4x4GB) and an SSD and now I have an old new iMac, which works great with Linux and delivers performance, which I never experienced with Mac OSX before.
If anyone decider to upgrade memory with these units, my recommendation is to also get "DIY Bundle 1.0TB OWC 3G SSD and HDD Kit for Late 2009 - 2010 iMacs" or the 2TB one. They are bringing a new life in your iMac and you don;t have to recycle it.