It is a dilemma tomorrow about updating to 2.0.
Pwnagetool will be updated very very shortly - we should be all able to update to 2.0 as long as your on an official contract (so you can activate it) but any unlocks will be relocked and the phone will no longer be jailbreaked.
It seems that pwnage will be updated very soon after the new firmware is out (probably within a day)... and personally if your planning on buying a new iPhone I would hold off on updating an existing one to 2.0.
Being in England like me - I wonder if the 3G phone will be out to buy tomorrow or if there will be a delay - if it is officially out tomorrow it is perfectly possible O2 could get deliveries of the phone in the morning and it could go on sale before the keynote - however that seems unlikely - It seems more likely it will be out on Tuesday UK time if there is no actual delay in sales because the phone is not available here yet.