At Lime Thinking we have been using Hudson as our continuous integration server. Hudson has now effectively forked into Hudson and Jenkins due to a dispute over the name with Oracle, the Jenkin's blog has details of what happened.
We will be moving over to use Jenkins as this is the community project and the version the existing developers will be working on. Upgrading from Hudson is apparently painless. I will let you know how we find this and of any issues that arise.