There's nothing that screams to me "must get immediately". Time Machine looks pretty cool, but I'm a little nervous about my co-workers abusing that feature to the point of frustration (for me, that is). IMO, Spaces is something that should have come with the first edition OS X.
While I am sure there are some bells and whistles worth having eventually, I think waiting few months isn't a bad idea. No matter what, it can't be worse than that other operating system.
And for what its worth, the new version of Ubuntu is pretty cool. I'm actually more excited about that upgrade.
Actually, please don't. Can't you guys please, please keep everything on the up and up for me? I'm begging you. I really don't ask for much around here by way of rules, but I'm a stickler for this one.