Based on the average amount of time before refreshes, there could be an update to the MacBook Pro. I'd wait 'til WWDC (although it's likely nothing will change), and then get it.
Otherwise, changes won't happen 'til October. Whether or not that wait is worth it is up to you.
There is evidence to suggest otherwise. The updated Whitebook now means you can get a 500GB drive in that, but not the Unibody Macs. Is that going to stick for 4 months (a suggested October update people are throwing around)? Doubt it.
Plus in recent times lappy updates tend to weigh in around 8 month gaps, so says the Buyer's Guide. We're just about to hit 8 months, unless Apple intends to throw out that timetable.
Add to that Snow Leopard. If Apple release new computers now, people will buy (and thus stop 'waiting'), then have to upgrade the OS later for a price. Releasing new laptops after SL's release (which is likely to be latest September) means lost revenue for Apple. And we know how they like revenue.
Also, Intel are set to release new mobile chips around now. On the assumption that they've stuck to their timetable, and Apple is still popular with them, we'll be seeing the new procs in updated laptops this month I suspect.
I know there's still a chance we'll see no update, but you can't ignore the above either.
Proc bump for sure. New nVidia chips were announced in Jan so, whilst I haven't been keeping up, I'm sure we'll see them in an update. Hard disk capacities would go up and hopefully a RAM boost for the MBPs since all the MBs now have 2 as standard.
But that's all conjecture, and I admit I could be totally wrong.
Reading the various comments is interesting to say the least. Yes there will always be a faster unit just around the corner, however it will be at a cost. A cost in money and a cost in battery life. Speed consumes energy. My humble advice is if the current units service your current and near term needs buy one and enjoy it. Computers have a life cycle so in several years you can again fester over the then soon to be released super new unit.