I too have installed the Yosh slip-on and have to say I love it. Due to my paranoid concern of valve burning and to decrease the erratic popping on decel I installed a power commander. With the stock fuel map on the module, I noticed a world of difference. Chiefly, the engine temp runs much more reasonably. It runs at 4/6 bars in town or on hotter days (90°F) and I don't think I've even seen the fifth bar. In addition, the popping was reduced to a bearable level. Most awesome of all, I got a noticeable power boost (~10% more) throughout the whole RPM range. As an added bonus, the exhaust sound is a lower pitch; more of a performance bike than a riceburner. All in all, I would say the power commander is the best value upgrade on this little bike other than changing the seat!
I do intend on installing an autotune kit to perfect the tuning, however I need to enlist the help of a good welder to replace the O2 sensor mount in the pipe.