Been using a MacBook for around three years now, running either MainStage or Gig Performer depending on the band and application. I've had some very minor glitches, mainly with one particular VST, but by and large it's been very stable.
I will probably move to a Mac Mini solution next year, not one of the new ones but a very stable late 2012 Mini that allows hardware upgrades. This way I can rack mount the computer and control it from an iPad. Less visible, less likely to get damaged or stolen.
SSD drives are becoming dirt cheap these days, so upgrade your Macbook's internal drive as it's then one less mechanical thing to break.
The one big advantage for me of a software solution is that I can change the controller keyboards depending on the gig without any change to the sounds. It also means I can just schlep along a cheap m-audio controller for rehearsals.