In case Visual Studio 2008 SP1 throws one of the following error messages at you

• Error 1 The Micro Framework installed on the device is of a version (0.0.0.0) incompatible with that of your project, which is v3.0  
• Error 1 An error has occurred: please check your hardware
• Error 1 Unable to communicate with device - TCP/IP:192.168.0.47:26000
• Error 1 Metadata processor exited with code: 255

please try the following things

• restart Visual Studio and retry (no joke, >90% chance it works)
• restart the hardware device and wait (8 seconds) until it booted up completely - then retry

Things that very rarely happen (if you know about them) are:

• Debugging single step (F10) breaks Visual Studio debugger on the AMI DevKit if you hold F10 pressed down.
• If you are not sure if your code really works correctly (e.g. unwanted endless loop without Thread.Sleep() or Float.ToString() and such) you might have to reflash your board (because your app starts automatically after booting and ends up in that error condition VS can no longer connect)