Plenty of experience with VPS systems -
Have a couple with webfusion. No problems so far but only six months in.
Have a couple with memset that we've had for four years, the occasional connectivity problem, but rare.
Had two with vpsland, don't have either any more. Lets just say I wouldn't use them again.
One with vpsville, no problems but we don't work that one hard - it's just there as a primary MX and POP3 server for one domain, plus test server for any development stuff we want to keep off of live during alpha.
All are running linux, either debian or ubuntu except one is on gentoo. We administer them ourselves via ssh, if they come with plesk or the like pre-installed we remove it.