Get one now. If your always thinking of getting the "next, new" thing, you'll be waiting forever. This is especially true in hardware, wear the increase in speed is barely noticable, at all.
Leopard does have many new features, but there will be bugs in the initial version as stated before, and Leopard's release is in spring. Spring could mean anywhere from late March to early June. And you could always upgrade. 🙂