The latest news from the Mac rumor sites says that closely following the release of Mac OS X 10.5 Leopard, Apple will also announce an update to the MacBook product line. Sources speculate that the update won't include major changes to the MacBook but will probably mean a small increase to processor speed. Early reports indicate this upgrade may not happen until November.
While a little extra processing power is never a bad thing, the reason we shouldn't expect a major speed boost is because Apple doesn't want the MacBook line to bite into MacBook Pro sales. Currently, top-level MacBooks run the Intel Core 2 Duo processor with speeds topping out at 2.16GHz. With the MacBook Pro processor upgrades earlier this year (featuring the Santa Rosa architecture) pushing speeds to 2.4GHz, we can't expect regular MacBooks to see much of an increase until the next generation of MacBook Pro widens the gap.
Like I pointed out in a recent Daily Download post, if you're in the market for a new Mac, you should definitely wait until Leopard is released October 26. With this new info, you may want to wait just a little bit longer for the MacBook to get an extra power boost.