On the other hand, it's difficult to imagine hardware being any more faulty or prone to failure than every iteration of the Xbox 360 in its current form, so if it were me, I'd wait for the Slim, hope for a slot drive and wireless built in, and skip even the possibility of joining the, RROD Brigade.
I've personally had both of my 360's fail twice and everyone I've known who owns a 360 has had it fail at least once, some many times.
I'm thinking that with the Slim a redesign will probably have been tested a bit more. At the very least, they may well have removed the Ring off the console so there'll be no ring on the surface to go red...