We had a debate&discussion at XP-Man on NoEstimates for which I did some notes. Reading the NoEstimates stuff, I was most attracted to the sense of "Let's not be satisfied with second rate" and of a thirst for continuous improvement.
I was left with the sense (possibly because I already believed it) that there are contexts in which NoEstimates works, and contexts in which it doesn't. But I was very glad to be provoked to ask in each case, "What value if any is our estimate/planning effort adding?" and "Isn't there a better way to deliver that value?"

What is an Estimate?

An estimate for a Project is (1) a list of things to work on; (2) a cost-range for those things; and (3) a list of risks, that is (3a) of Dependencies that 1&2 rely on, and (3b) of things that might cause significant change.

An estimate or plan for a sprint is (1) a list of things to work on, (2) a "cost" (eg story points) for those things and (3) a list of things we are uncertain about, or (4) need to get help with.

The value of a project estimate is to feed-in to (1) A go/no-go decision and (2) seeing things we want to see sooner rather than later (e.g. should we hire more people, do we need help from specific 3rd parties, is releasing in time for Christmas possible)

The value of a sprint estimate is, to see things we need to ask for in advance (ie external help or resources); to give everyone a sense of confidence about what we're doing; to fail-faster, that is to see sooner what we can't achieve.