My experience w/GripShifters is similar to this. The lower-end are poor and need to be babied to work; the top-end ones I got for my "good" mtb are fine (though I still dislike installing new cables).

I'll second what's already been said regarding inexpensive trigger shifters out there - I recently tossed an old set of very worn GripShifts (400's, I think) and a worn LX rear derailleur, in favor of a set of SRAM X3 7-speed shifters (€25) and an SRAM X4 rear derailleur (€16.50). If you can spare the €50-ish, to me it's worth the change, removes a lot of headaches.