We went to WDW last year for Valentines Day.

There isn't really anything specific going on that is special to Valentines Day. When you make your dining reservations you have to secure them with a credit card because for dining purposes they do consider it a holiday. I think some of the restaurants do have special holiday menus. Here's a link to what was offered last year.
http://www.allearsnet.com/menu/men_valent.htm
We had dinner at the California Grill which was lovely & very romantic-but you have to make sure & call at your 90 day window because it might be hard to get.
We stayed at Port Orleans Riverside-which is a very romantic resort I think & they have carriage rides which I booked for Valentine's Day right before our dinner.
You might see a few nice window decorations geared to the day, but not much else.
Have a great time. If you have any more questions let me know.