There will be two schools of thought that you'll see posted here.
School of thought one says wait for the Merom Macbooks. Odds are that relatively soon they will be out and people will advise you to wait "if you can."
School of thought two says buy now, because there is always something better coming and waiting for some mythical rev is silly.
What school of thought is right is up for debate, but I don't think anyone here will advise you to wait for leopard. You could be waiting until April of next year for all we know. The real decision revolves around the next Macbook revision. It is very very possible we'll see a rev of the MB very soon. If you can stomach not having the latest and greatest, or need the Macbook now, go for it. I personally think the consideration of future hardware in this environment is silly. There is ALWAYS newer things coming out. The current MBs are very sweet, and performances gains with the C2D chips will not be revolutionary; they will be evolutionary.