there's some really really really fast flash sticks out there, on the order of sustained 25 MB/s . i've someone managed to avoid programming flash, so I dont know for sure, but I'd wager that whatever column/row addressing scheme is inherent to flash, its nothing compared to the 9ms access time on a hard disk. In other words, it'd probably make a pimp-fly swap drive.
I use utorernt on my windows machine, I'm doing three 6GB files... 7620k VM size, 4mb in ram. Thats windows tho. I never checked the resource usage, but rtorrent which i used to use "felt" very lightweight and allowed much smoother operation on my 256mb ram laptop.