What is the maximum app size allowed?

Notice that there are two methods to choose from when it is time to upload an app?

You can use the upload form via ITC or 'Application Loader'.

Application Loader allows you to bypass the webpage upload mechanism where large files can be lengthy (w/no progress indication) and/or problematic.

I've heard the max file size for a compressed app is 20mb. That is untested and unconfirmed by me however, so you may want to take it strictly as rumor until/unless you test or learn differently for yourself.

Myst 727mb

Good point. Wonder what it was compressed...

My understanding that if an app is larger than a certain threshold (50meg?) then it won't be available to download over the 3G/EDGE network. Any apps larger than that would have to be downloaded through the user's home broadband connection into iTunes, and then synced into their devices.

Other than that, there's no real size limit, other than physical storage on the devices.