Creating patches for software updating

Hello.
What tools/approaches do you currently use to provide your customers with the latest version of your software product or any other freshness-critical files?

If you currently use any self-made tool or approach then do you think of changing it to some standard solution?

What features do you think an ideal patch maker must provide (including both patch building and applying aspects)?

What do you think can be the main reason/advantage for using a patch building utility to provide your customers with compact patch modules (containing only differences between files) instead of full-version software packages?

Did you try PatchFactory by AgenSoft (www.agensoft.com)?

Thanks in advance.