That's just it: with a vertex 3 and a maxed out CPU the x220 doesn't perform like a thin and light -- I'm getting the same IO performance as a vertex 3 in a desktop, and although I could get a CPU boost with a desktop processor I'd have to give up on having all my work with me at all times / at conferences.
The EC2 option has always interested me, but short of EBS RAID its IO actually isn't better than a vertex 3 -- they're crazy fast; if you haven't tried them I highly recommend you do :)
