If you are looking for an authentic downtown similar to a South Beach or Ybor City, P.I. and Citywalk don't come close to downtown Orlando. The heart of activity of downtown Orlando is around Orange Ave and Church St and then heading North up Orange Ave.
Be sure to check out Wall Street Plaza that has 8 different bars/clubs:
http://www.wallstplaza.net/
Also, take a walk around Lake Eola and the shopping district of Thornton Park in downtown, which is in walking distance from Wall Street Plaza. Another area that is a lot more low-key, but has some upscale wine-bars to check out is Winter Park:
http://www.parkave-winterpark.com/html/restaurants.html
This is more of a restaurant / wine-bar scene and does not have any nightclubs
Stating that, you won't find anything else like Downtown Disney or Citywalk anywhere else other than maybe Vegas, so it is fun to walk around, but the clubs are generally filled with non-stylish 40 somethings that don't typically frequent bars at home (sorry to all you 40 somethings out there - I'll be there soon enough). If you are to be in Orlando a week, I'd do Downtown Disney / Citywalk / Winter Park on the weekdays and Downtown Orlando on Friday and Saturday night.
For some good dining that isn't touristy but is still filled with tourist and locals, check out Restaurant Row on Sand Lake Road, about a mile west of I-4. Amura and Season's 52 are a couple of nice restaurants to visit, but there is also about 30 plus other restaurants and bars in this area, some of which that have patio area's on Lake "Little Sand Lake" (Season's 52 has a great patio seating on the lake). Restaurant Row isn't a name of a plaza, but rather the area in general in this part of Orlando.
-- Scott