I run XP64 on my SSDs without issue. Applications load instantly and the general feel of the system is much faster than on a platter based drive.

Many people have issues with freezing and stuttering when using an OS on SSDs so I think the results can be mixed, depending heavily on your hardware and OS flavour. Using a normal platter drive will be the most reliable option for now, until Windows 7 appears on the scene with certified SSD compatability. Couple that with an SSD array for your wow clients and you've got probably the best drive setup for multiboxing wow in todays harsh dalaran-like environment