I've talked to NetBSD people about EC2 a bit, but I don't know their current status. IIRC at one point they were limited by a lack of SMP support in their Xen-PV code, but I don't know if that's still the case.
I have a couple of boxes at home right now running NetBSD as dom0 w/xen3 and linux/freebsd/netbsd running as PV guests if I get a chance I will move them to some more modern HW and see what happens with NetBSD and multiple cores... Think one of them is a dual core right now but gotta check...
In any case NetBSD PV Kern on a small AWS might be a great combo for cheap BSD thrills....