hi azrel,
many rumors on these boards point to the possibility of there being powerbook updates in september, at the mac expo in paris. this is towards the end of september.
however, many think that any updates that the expo will bring will be very minor, and the current 15" powerbook is a fantastic machine for the price....and i am not lying about this, because i bought one last week for uni puposes also.
if you need it for the start of term, get it now, but if you are prepared to wait longer for updates that have a 50/50 chance of showing up at that expo, then do so. it depends on your balance between need/want.
the truth is, nobody knows for sure, ecept steve jobs and his crew.
i also took advantage of the student union deal, and got a 4GB green ipod mini. im expecting delivery of all this stuff as early as next week.
remember, the current powerbooks are killer machines!!!! especially the 15" and 17", if you were considering the 12" i would have told you to think again.
remember, if by freak chance the powerbooks get majorly updated
then expect long lead times for delivery, so you may miss out on the student union deal (mail in rebate by the 8th, as you say) and it may leave you at uni without a powerbook for longer than expected
hope i have been a help
tastic