There is more information about handicapped parking in the disABILITIES FAQs thread near the top of this board (or follow the link in my signature).
Also, we have found that the handicapped parking lots can sometimes fill up.
At Epcot, there are 2 areas, and they route guests to the second one when the first fills up. So, don't be surprised if you are directed to different places if you go to Epcot more than once. Some of the spots are pretty far out, but still an OK walk for someone who has a mobility device with them.
AK and the Studio have fairly small handicapped parking lots for the amount of people parking. At both parks, DH has needed to drop DD and I off and then go park because the lots were filled. This may not happen to you, but it is a possibility, so it is best to know so you can plan where you would meet up.
For MK, most guests staying on Disney property take the bus from their resort.
If you use the parking lot, you have to walk to the Ticket and Transportation Venter, then catch a boat or monorail to MK.
By using the buses, you cut off the boat or monorail step and end up dropped off close to the park entrance - near to where the monorail and bus drop guests off at MK.