Mine are all in ALAC. I initially had them in WMA Lossless thanks to a 200 CD batch ripping setup I had. I would load a changer with 200 CDs and it would rip them to a PC and find the album covers.
I then converted all of the WMA Lossless to FLAC to use in my car. I had something called a Phatbox in the car back then and it could not support WMA lossless.
The FLAC was then converted to ALAC thanks to a new car setup that utilized the 160GB iPod Classic. I used Foobar2000 in batch convert mode to get them all into ALAC. Now I mainly rip to ALAC. (I should mention that I still have the WMA lossless for Windows Media Center and FLAC for a Sanza Fuze)
The main reason I chose lossless is that I don't think it makes sense to archive in lossy formats. While I don't think there would be much difference between 320kbps and ALAC, I really don't have time to blind test every song in my library to be sure, and since hard drives are cheap, there isn't much reason to worry about it. Also, if a new CODEC comes to market that significantly beats mp3, you have the lossless file for transcoding to it without losing data. You do not have that option with lossy files.
Even on my 32GB iPhone I have lossless files. I know it is easy to convert on the fly, but I don't have any reason to. I have a subscription to MOG that uses 320kbps and I can just download their files to my iPhone if I want more than the few albums in my own collection.