1. If you go from 32 bit to 32 bit or 64 to 64 most will be fine. Some like antivirus should fail. Uninstall before upgrading.
2. All browser addons are going away. Count on that.
But you should have your disaster plan at the ready. If you change from 32 to 64 bit then it's essentially a clean install and no install apps survive.
If I upgrade from Vista to Windows 7, do I have to reload all my programs or will they function normally?