Is it bad to install and uninstall programs constantly?

No, not at all. Of course, installing apps will slow down your phone a tiny bit if it's a newer model (like 2 ghz, 2 gigs ram) and a lot if it's an older phone <1ghz, <500mb ram) and uninstalling will speed it up because of background services that apps have that run all the time in the background.

Also, restarting your phone once in a while is a good thing, it gives the OS a chance to clean some stuff up and it reloads everything.

No it's not bad, but it takes up memory on your temporary drive.

PC's store information from programs on a central hard drive, which allows the information to be accessed from the program when you start it up. If you delete the program to the recycling bin, and then empty that, you will still have bits and pieces of that hypothetical program on your computer. A PC leaves a trail behind when you delete a program, and only the "pointers" are erased when you delete something. The physical memory itself awaits to be replaced by other data downloaded or installed at a later time.

Skip to 1:30 and this will explain everything: http://www.youtube.com/watch?v=G5s4-Kak49o