Did someone forget to use a coaster? If you have a water stain on your wooden table that's causing you grief, a hair dryer can speed up the removal process.
Homemade Mamas explains the process:
Rebecca found this guy on her coffee table and thought the table was ruined... We used a blow dryer on high. We held it fairly close to the stain. Slowly it stared disappearing!
After about 20 minutes the stain was almost completely gone. We put a little olive oil on it to moisturize the wood.
We haven't had a chance to test this one ourselves, but a quick search reveals that a lot of people have used this with success, so it's worth a shot if you're desperate. You could also try mayonnaise (a popular but slightly grosser alternative), as well as toothpaste. Different tables may react differently to this though, so try at your own risk!
Agghhh!!! Water Rings! [Homemade Mamas]