As you probably know Windows Mobile 6 has been announced, along with a new SDK. The SDK doesn’t seem to be available yet, but according to the What’s New for Developers Guide, you can use the new emulator with WM 5.0 development.
WM6 is also fully backwards-compatible (it uses Compact Framework 2.0 SP1) so any WM5 app that doesn’t use a lot of esoteric code will run just fine as it is on WM6.
edit: Turns out they dropped the .0 from the version, so while it is Windows Mobile 5.0, the new version is just Windows Mobile 6…
