Strengths: Smaller and apparently more accurate than most GPS systems. Wealth of functions / settings makes it ideal for almost all situations.
Weaknesses: Occasional problems with signal in built up areas and areas with lots of tree cover. Still a little heavier than you might like.
Overall: The one piece of equipment that has revolutionised my training more than any other. Before having a Garmin I used to run around aimlessly doing mainly junk miles and having no idea whether I was progressing. Since buying it running a marathon seemed like a good idea and I'm sure I wouldn't have done as well without the accuracy of training records thanks to the Garmin.
Weaknesses: Gets a bit statty at times, but only briefly.
Overall: Fantastic book that every runner should read even if it's only to convince yourself that fell running is definitely NOT for you (it sounds like there's way too much pain involved!). More please.