It looks like php 4.4 just came out on July 11, so it's still pretty new. I don't know of anyone who is using b2evolution with it. And there's no way anyone can give you assurance that an upgrade won't break something. Back up your database and your files before the upgrade. If anything goes wrong (and it probably won't) then you won't lose anything.

The [url=http://www.php.net/ChangeLog-4.php#4.4.0]changelog[/url] shows that it's mostly bug fixes. I don't think you have anything to worry about.

Looks like I may be one of the earliest to find out :-(
The upgrades are happening to prevent conflict with one of the libraries, and so far, the servers which have been done have only caused problems for Simple Machines Forum.
Will back up and keep fingers crossed!

Good luck. Report back here and let us know how it goes.