I was there two weeks ago, well worth a visit just to see the random peanut shells all over the floor! The Singapore Sling is worth it too! We went dressed up, and the majority of people in there are, but I don't think you need to be dressed up. It just makes the occasion a bit more special I guess!
After going there, I would STRONGLY recommend going to the other great bar in Singapore, think it is called Equinox, for a cocktail or two. It is very near to Raffles, on the 70th floor of a skyscraper! AMAZING views of the city and beyond, we went just before dusk (so 5pm ish) so we saw it in daylight and night.
Enjoy! I loved Singapore, think it is a great place for a few day stopover en route to Australia or wherever!