I'm wrapping up my 3 night trip to Manila. First of all, I'd like to thank everybody for their input. It really helped out with my trip planning, and what would have been 2 nights, was extended to 3.
I stayed at the Intercontinental. While the service, location, and Lounge was excellent, all the rooms (at least the 4 that I tried) are quite musty due to mildew (or smoke floating up from the smoking floors). It's just an old property. I should have booked the Shangri-la.
Makati is depressingly surrounded by Western restaurants. Seeking out Filipino restaurants require a bit more work. Traffic is horrendous enough that I'm almost temped to eat at Bubba Shrimp's tonight

The MRT is even worse than sitting in traffic - it's so crowded it's almost impossible to get on the train during rush hour. In fact, there's usually a sizeable queue just to be let into the station! But hopefully I can summon the courage to make it to Cafe Juanita tonight.
I would recommend one day for Manila itself - the American Cemetery, Fort Santiago, and Intramuros are about the only attractions.
I did a day trip to Corregidor. You board at 7:30am, and arrive back in Manila around 3:45pm. The ferry takes 75 minutes each way, so you get about 5 hours on the island (including 1 hour for lunch). The entire tour is guided - you're taken on these trams throughout the island. Very worth doing. If you go, check out the shrapnel marks on the cannon barrels.
If I had an extra day, I'd go to the volcano as well. All in all, a very worthwhile destination.