I also had my Outfitter rudder control handle pop off today while kayaking in the Gulf of Mexico off Florida. I purchased the Hobie Kayak in July 2010 and only had it out 6 times. I had not touched the set screw since it was installed new at the Hobie factory.
This is certainly a design flaw or a manufacturing problem. A couple better designs would be to either have a handle made of stainless steel which would hold the set screw or to have a solid plastic handle which allows for a screw with a locknut to attach through a hole in the rudder control shaft. Also, the steel rudder control shaft could have a geared top to better support the force on the rudder control handle.
I will likely receive a new rudder control handle from Hobie, but I do not have confidence that it will work for very long. Maybe Hobie can send me a spare to carry in my kayak until they resolve this issue.
I have attached a picture of the failed rudder control handle.
Please post to this forum if you have this issue (also check your set screw and see if it is loose and ready to fail).