I disagree with the last post! (sorry!)
If you get a decent rack case, they're not fragile! And as for set up and leave? I agree once you've got your signal routing sorted i'd leave it be, but you can then program the thing to do pretty much anything. Take a Mesa Triaxis, 2:90 and a G-major and you can get pretty much anything out of it.
As for what rob has said. Instead of buying two poweramps, why not just split your rack? Put the poweramp in another case and your preamps and effects in the other. Then take the preamp case to practice and plug into the PA, and when it comes to gig time, put it ontop of the power amp case (easy if you get cases that interlock well like the gator ABS ones) and plug em up. If you're clever about it you can make them plug and play. Oh, makes them lighter too
What i like doing in a rack is having a 1u panel on the back with neutrik power and jack connectors (the locking types) and that way its like a plug and play unit. Very handy, very quick and looks pretty cool too.
S