http://mark.rehorst.com/Strobe/strobe_schematic.gif is a schematic showing how I use it to switch 50us wide, 15A current spikes through a 5W LED. A slightly more complex circuit would speed up turn-off time by actively draining charge off the gate.

BJTs are usually cheaper then FETs and are very common in the gadgets you would be scrounging parts from as a starving electronics hobbyist.

Note in the lecture notes that adding a resistor to the emmiter leg of the transistor presents additions to the equation. The explanation above is for common configurations where there is no resistor there (which would work for just about any application where you are taking i/o from a microcontroller). This drastically simplified the equations necessary.

These switching issues are also present with FETs and are a major source of inefficiency in switching power supplies.

I did a quick search for other online material about BJT and FETs and found this set of Lecture notes from OU.
http://www.nhn.ou.edu/~bumm/ELAB/Lect_Notes/BJT_FET_transitors_v1_1.html

Arthur: Agreed, that would be a good application for a much higher current carrying application, but for our purposes here, it is very, very overkill. One of the reasons I might want to use something in that application, is for a PWM switching device, such as Chucks instance (JFET’s would work okay too). The switching capabilities are much better, but, you also have to remember your price per unit drastically increases when you add speacialized transistors where generalized ones will do. If I were carrying that much current on the same bus as a microcontroller, I would be concerned with how much noise it is likely to produce on the bus. For communication signals, and low power applications, the BPJ does just fine. I realize not everyone agrees on the same methodology, but that is my opinion, and nothing more.