I saw my OB yesterday and actually asked this questions and he said he would be suprised if I was feeling consistant movement everyday. He said it is totally common to have a few days of a lot of movement and then days where there is little none. He told me not to worry unless I am cramping or bleeding.
Thanks for posting this - yesterday my little guy was moving around like crazy - today not so much. I am only 18 weeks, so I know it's way early for consistent movement, but I've been sucking down ice cold water all day and eating lolli pops - Guess I'll stop shoving candy in my mouth now :)