I use Aperture, but not exclusively - I prefer DxO for RAW conversions. After conversion, I import the RAW files into Aperture as referenced files in one library (stored in year/month folders) and the jpgs directly into the Aperture library. The RAWs are backed up on multiple external drives.

I'm not yet at the point where I need to save space - the 500 GB drive helps there. But when I do, I'll just delete a year at a time of the RAWs from the internal HDD.