Ainge did not let Tony Allen walk. He offered Allen more money than the Grizzlies did. TA wanted a bigger role and didn't want to play behind Pierce and Ray. That's not Danny's fault.
Got a source for that? Because my recollection and articles I just Googled from that time period say differently. For example, this article says we initially offered just a 2-year contract, then only matched Memphis' offer, not exceeded it:
"We [eventually] offered Tony the same deal that he ended up getting in Memphis, but maybe ... [if] I made that offer initially [Allen would have signed in Boston]. But we were trying to maintain our flexibility, not this summer, but the following summer. It wasn't about money. It was about years and flexibility."
http://espn.go.com/boston/nba/columns/story?id=6560546&columnist=forsberg_chrisIt's possible we offered more per year on that 2 year deal, but I can't find anything to confirm it, and that's not really the same as more $ overall.
TA for me is the last significant bad decision as well, outside of our draft busts. It's really been awhile since we made a bad player move, though it's easier when you're rebuilding and the stakes are lower.