I loved timing mine though, I don't know why, but it felt theraputic LOL! Trillian has described contractions much better than me!

I knew my very first contraction with DS1 was the real thing because it felt different to a BH and it built up, then went away. It kind of felt like a balloon was blowing up inside my tummy and then slowly deflating. It would be nice if it felt that way all throughout the labour! Luckily labour is clever and slowly builds up in intensity (for most people anyway!) so you have plenty of time to get used to it.