In reply to Antigua:
If you're bothered by crowds at the start, go for smaller events. Big city races are often very expensive and very crowded, whereas smaller events are cheaper and less crowded. I prefer smaller events, partly for the reason you suggest, that it's easier to run at your own pace.
Smaller events are often organised by running clubs, whereas the big city events are usually run by commercial organisations. There are pros and cons to each, but in my experience, running clubs do a great job of organising their races - years of experience in many cases - and I would usually opt for a race run by a club over a commercially organised race. There are exceptions of course, but the worst races I've done have been organised either by a commercial events organisation or a local council.
Have a look on EntryCentral - it's a race entry website and it will give you an idea of the numbers of runners in races. We use it for our club races - Crieff 10k trail race and the Strathearn marathon.
If you like running, races can be a terrific experience. I love them, even when I don't do very well. There's often a great sense of community and mutual support, and running with other people will always make you perform better.