This is a bit of an annoyance: double-clicking a Unity iPhone scene opens it in regular Unity (2.5), and Unity prompts me to upgrade the project. That wouldn’t be so bad if Unity didn’t then automatically set that project as the startup project! When it starts up now the only options are to upgrade the project (and probably screw it up) or to quit, so the only way to open Unity “normally” is to locate and open some other project.
This should be fixed by adding a cancel option to the Upgrade Project dialog, instead of just upgrade and quit.