If you're expecting your app to get used by folks in all sorts of environments, I'd strongly encourage you to figure out how to host it on port 80. Everything else is going to get blocked by one sort of firewall or another. About the only port that just about every company allows open is port 80.
My personal experience with this comes from having hosted a Silverlight-accessible web service on a non-standard port (port 4502, though it doesn't make much difference). Because of Silverlight's networking limitations we didn't have much of a choice, but we ran into a whole bunch of firewall issues at one company after another after another. Do yourself a favor and just host it on port 80.