The 99 & 100% response times are most interesting for debugging our problems.
What client & timeout value are you using? I'm using the erlang client where the default timeout is 60 seconds, but I've over ridden that and am using 2 seconds.
Interestingly, over the weekend I've started to see a few put & get timeouts on the application side, but the longest 100% response time is just under a second which points to a network delay.
I'd start by polling these stats and then examining when you get an application side timeout. Maybe check the size stats too, if you can catch which key the operation timed out on it'd be worth checking the object size & sibling count for it. If nothing else this would eliminate the possibility that it's unique to a particular object.