Are you looking at MB or MBP?
Purely speculative on my part, but I figure that the MB will probably get the SR bump (because that will have to happen two months after I buy my laptop - it's scientific

) and any changes to the MBP will be minor. Nothing from Intel makes it sound like anything new will be out before November - so it might even be a Leopard Launch in October and then the usual 6 month revision cycle in November. If you need a new machine, you need a new machine - Leopard or no Leopard.
Personally, I think that the whole "wait for the best" quandry that so many Mac (or future Mac) owners face (myself included - I originally planned on buying machine after the MBP's were released in June - it took me another 6 weeks to do what I knew in my heart would be my financial reality back in May) is really, really unproductive and in many ways - kind of destructive. It takes a lot of the joy out of a process - and more than any other computer, the Mac is really a joy to buy. I mean, I'm a gadget junkie - like a HUGE, HUGE gadget/electronic fanatic - toys of any type get me excited, but I haven't been this excited about a toy, as I have with my MacBook in years and years. The last time I got this much pure pleasure out of something like this was probably when I bought my first DV camera my senior year of high school. And yet, my joy was tempered a bit because I can't help but question "what will come out next; what if I could have waited; what if I had just sucked it up and asked for the extra $400, etc."
And the internet doesn't help - actually, the internet is the problem. Sites like this are a breeding ground for people who like to get the best value they can while also being the most advanced (and again, I'm totally one of those people). Apple is a particularly problematic company because a) they appeal to even non gadget junkies the same way they appeal to people like me who live for toys b) the brand itself is elite and has a sense of gravitas to it that makes the purchase seem more important and more serious than buying a regular computer, even a really nice regular computer, thus the decision to "get it right" and lessen buyer's remorse (or not remorse, but future product envy) as much as possible and most importantly C) the fact that the model line-up is so limited and updated only twice a year (and major changes to design are much less frequent) - no one wants to get stuck with "last year's model" mere months before the new revision comes out.
More and more, I think that all of those factors go into creating emotions that aren't entirely healthy or useful (at least for me) - and ultimately, detract from the enjoyment and you know, the purpose of the product itself. If you are always waiting for the next thing, you'll always be waiting. Here it is four days after buying my laptop and it's taken me to type this up to fully resolve being OK with getting a MacBook rather than a MacBook Pro (which I didn't need - honestly - it's not like I won't be getting a new computer in two years anyway, the only reason my last laptop lasted so long was because I built a cutting edge PC rig two years ago that only recently went on the blink - really, really inopportune timing - but still) - and I haven't had as much fun on a computer in ages and ages.
Anyway, sorry to be so long-winded - but it's just up to you - how much do you need a new computer? I just wouldn't let future "what if's" impede any pleasure you could be having NOW.