So, Yesterday I helped out a friend with a talent show. She had asked me to play guitar with a band for a couple of her songs. After a rehearsal I decided that I would try my little 5 watt BlackStar ministack amp for the show rather than my 150 watt behemoth of an amp, and I was presently surprised. It sounded GREAT! It provided all the stage volume that I needed, and after I planted an SM 57 infront of it and sent the sound out through the house PA system, it was loud enough for everyone to hear. This experience has proved to me a suspicion that I have had for a few years now. All you kids who need 300 watt guitar amps are falling for the classic 'more = better' idea, which may just happen to be false in this case. Nobody NEEDS a wall of amps with thousands of watts. For most musical styles, A good 50 will do just fine in any jamming situation and live, you may need even less. So my conclusion is this. You don't need to buy that 100 watt + amp. In fact, later you'll probably find out that it is a little inconvenient. It weighs more, and only sounds good after its been turned up too loud to hear the drums (unless you use an expensive and often tone sucking attenuator).
There are a few exceptions to that rule, like if you don't have a PA (then your vocalist is up the creek and you are doomed to 'ear out' the sound levels from a stage) or if you happen to be someone like Gus G who seems to need six 200 watt monsters on stage with him wherever he goes.