AnandTech found evidence that AMD is working on a B3 stepping for its Bulldozer processors. Perhaps the new stepping will somewhat improve the performance of the chip, but the site adds that if the past has any meaning, a new stepping won't arrive anytime soon. For instance, the C3 stepping came about 9 months after the release of the Phenom II X4 with C2 stepping.
The initial CPUs use B2 stepping, but an AMD BIOS and kernel document already shows reference to unreleased B3 stepping. A stepping update should bring improvements (usually minor) to performance and power consumption, as well as possible bug fixes. Stepping updates are a normal way to provide small upgrades in between bigger ones, such as die shrinks and microarchitecture changes. While B3 stepping may help Bulldozer a little bit, it's very unlikely that a stepping update would provide huge benefits and thus make Bulldozer significantly better than Intel's equivalent CPUs - so waiting for this update is not exactly a good idea.