Some pitch the whole thing.
Some discard most of the liquid and pitch the sediment.
If I make a 1 liter starter, I prefer to pitch the whole starter at high kraeusen (peak activity) about 24 hours later.
If I make a 2 liter starter, I prefer to pitch the slurry (sediment) and just enough liquid to make it pourable.
Cool in the fridge for 12 to 24 hours to get all of the yeast on the bottom, pour off most of the clear liquid, then allow to warm up to room temp before swirling and pitching.
The clear liquid doesn't really have any good flavors, 1 liter is about the most you can add to 5 gal without detrimental effects.
Edit: The above applies to starters made from liquid yeast.
If you're using dry yeast, re-hydrate in 1/2 cup previously boiled and cooled water at about 90*F. Wait 15 minutes, stir, and pitch the whole deal.