Matt Yonkovit has started a series of posts on Tokyo Tyrant at Percona's MySQL Performance Blog. Great in-depth analysis of the reliability and performance of TT.
Part 1: Tokyo Tyrant -- is it durable?
Part 2: Tokyo Tyrant -- the performance wall
Part 3: Tokyo Tyrant -- write bottleneck
(parts 4 and 5, about replication and scaling, are hopefully coming soon)