Update 2:
New development build b816 with Minecraft 1.6.5 support is now available.

Notable changes include:
Fixed beds.
Fixed issue with arrows crashing clients and servers.
Multiworld is DISABLED (this does not include built-in nether portals) pending investigation.
Fixed inventory updating through plugins.
Fixed entity already in chunk errors.
and Multiworld is DISABLED (this does not include built-in nether portals) pending investigation so please don't report issues with it.
This is a non-recommended development and test build. You will not receive support outside of bug reporting. Backing up your server and completely understanding the risks of running this build is highly recommended before you run it.

Once again, we cannot guarantee that this build will not completely corrupt your world or cause a disturbance in the force.

If you completely understand what you are getting into, you can download the latest development test build with this link:
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I wouldn't update becuase it just seems like a test build and saying it could maybe harm your world
im not updating my server anyway

I updated when i had a new world on and all the plugins and stuff worked fine and there was no problems so i put my real world and still fine so But 1.6.6 is out so :\

Hmm im not to sure if its worth the update i think bukkit might start getting a recomended build now that 1.6.6 is out