10 Things you should know to develop Windows Mobile 6.5 applications

1. The 6.5 Developer Tool Kits has been released: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=20686a1d-97a8-4f80-bc6a-ae010e085a6e
(don't forget to install the WM 6 SDK(s) first)

2. You need to include gesture.h, GesturePhysicsEngine.h & WindowsAutoGesture.h to handle gestures in your apps and games (touch screen devices only)

3. Gesture samples projects get installed with the 6.5 Dev Tool Kits - C:\Program Files\Windows Mobile 6 SDK\Windows Mobile 6.5 Developer Tool Kit\Samples\PocketPC\CPP\win32 by default

4. WM 6.5 Supports Widgets - since its already explained here I won't re-write it:
http://blogs.msdn.com/windowsmobile/archive/2009/06/04/getting-started-with-widgets-on-windows-mobile-6-5.aspx

5. New Start Menu icons are 45x45 pixel PNGs (90x90 for hi res and 60x60 for 128dpi). 32 bit images and transparencies are supported.

6. PNG "icons" can be placed anywhere as long as you have the appropriate registry key: "HKLM\Security\Shell\StartInfo\Start\MyCoolApp.lnk" In that key create a string value named "Icon" that points to your png (ie \Windows\MyCoolApp.png). You'll need to be clever about supporting multiple resolutions during installation.

7. The only professional square emulator provided is a 128dpi 320x320 resolution. So hopefully no more 240x240 touch screen devices.

8. The new Today Screen is just a plugin so it can be turned off if you're trying to make today screen plugs (although this might upset your customers).

9. Windows Mobile 6.5 is still built on CE 5 so you can use the WM 5 SDKs to develop if you don't need the new features. (and honestly you can still use the 2002 & 2003 SDKs if you want but its a hassle if you need to debug on newer devices).

10. If you're feeling brave and don't mind bending the law you might be able to upgrade your current WM phone to 6.5 by searching on http://www.xdadevelopers.com/ (at your own risk)


** Update **
There was a mention of 36x36 and 64x64 png icons needed for 96dpi devices and some of the other sizes will be used on multiple devices. I'll post further details as I find them.