Sure, Apple's iPhone OS 3.1 includes a couple of new goodies like iTunes-based App management, but if you like your Jailbroken or Unlocked iPhone, sit tight until Dev-Team gives the all clear. You could otherwise lose your unlock for good.
If you update to Apple's new software using the normal iTunes process, you will lose your ultrasn0w unlock. In fact you may lose it permanently, because for most people the baseband firmware cannot be reverted to a previous version (unlike the main application CPU firmware).
But don't worry…our PwnageTool program lets you update your main firmware without touching your baseband firmware, so you can still have the best of both worlds.