I'd second the wait response. Why spend money upgrading to Leopard if you can get with your nice new machine?Personally I'm waiting it out.
If you buy a new macbook now I'm sure it will be quite nice.
*however* if you're current computer is still functioning, try downloading onyx and running a system cleanup with it, and then just holding out a bit more.
I feel that the next upgrade that will come out will be awesome. A new operating system upgrade with such a revised interface seems to yell product revisions to me.