Avoid doing anything you might read in tourist guides! Apart from the Portugese fort, Tree of Life and the National Heritage Museum (Did I get it right?) there isn't much to see. If you want a good laugh, drive towards Sar (Saar) on the Budaya Highway until you see a brown highway sign that says 'Weaving Centre', that's probably the most hilarious thing I've ever seen (I will scan a picture of the place soon!). What you should do instead is to go to some of the night clubs in Bahrain, there are about three or four worth going to, score some chicks and then fly out of the country the next day! ;-) Seriously though, unless you live here (like I did for a short while) there isn't really much to do. If you want to shop you're better off in Dubai (U.A.E.) than here although you can make bargains in the souks if you're down with the bargaining game.
Fondest memory: Old Beans is the place I miss the most, the smallest, dodgiest bar/pub/? in the whole of Bahrain. This place is in Adliya, hard to find even if you live in Bahrain, if its of any help its close to a Irish-style pub (there is only one in Adliya if I remember this correctly) and they should know how to tell you the direction to Old Beans. Go there and see what I mean!
My Favorite restuarant was Al Arisha which is located in an area called Umm El Hosom. It's famous for Lebanese Meeza (Appetizers).
Fondest memory: If you visit Bahrain during December & March period, make sure to pass by the beginning of Sitra Highway to view the Flamingos on the left and right sides of the bridge