Delayed or Just Laid Back?

When do you start to worry about your child's development?  On one hand, Bub has always been an incredibly laid back baby and it's easy to chalk everything up to lack of desire.  On the other hand, he's almost 11 months old, not crawling, not pulling up on anything, won't drink from a cup, isn't talking, and I'm probably forgetting something.

As much as I'm trying to stay relaxed, it's hard to not get worried.  What if he's NOT just a laid back little boy and I wait to get him help?  We live in such a world of early intervention, should I err on the side of caution and bring it up?

Then, I remind myself that numerous people have told me it's not unusual for younger siblings to do things later and I feel like a dolt for worrying.

This mommy business isn't as easy as Hollywood would have us believe!  Any moms out there have any sage advice one way or the other?