There was no BB update in 4.0.1 so you should be able to upgrade if you want but the tools will need to be updated.
You should be able to obtain your SHSH using umbrella [not for 4.0 though]
That's why I'm in no hurry to update to 4.0.1. I wasn't as interested in jailbreaking when 4.0 came out, so I updated. Now, I wish I hadn't. I know that there are ways to downgrade back to 3.1.3, but all of the tools seem to require SHSH blobs. I've got nothing. What the hell was I talking about? Oh yeah.
To the OP, if you want to jailbreak, wait. If the jailbreakers say it will work with this lastest update, then update then JB. if jailbreaking is not on your "to-do" list, then just be patient.