Depends if you've got the cash to spend now, or not. The OS update will have no impact on the price, but should make the N800 more desirable than it is now - you will be able to upgrade the OS yourself (it's *very* easy to do) as long as you have a PC or Mac.

Other than your finances, I see no reason for you to wait until the next OS - get more value for your money by purchasing now, don't wait.