I learned this the hard way when Froyo finally hit my Motorola Droid last night. I excitedly waited for the upgrade to complete, only to find my phone unresponsive and full of force closes when it finished. And it turns out HelixLauncher was squarely to blame.
HelixLauncher + Froyo = Trouble
HelixLauncher, if you aren't familiar with it, is a popular home screen replacement app for Android. Unfortunately, it appears it hasn't been updated to play nicely with Android 2.2 -- and if it's on your phone when Froyo rolls in, you're going to be in for a serious headache.
I was actually lucky: After isolating the issue and identifying Helix as the culprit, I was able to switch back to Android's stock launcher and get things in order without too much hassle. Once I managed to remove Helix from my system, everything ran as smooth as, well, frozen yogurt.
Other users have had worse experiences. Surfing through various Android forums, I've seen reports of folks getting stuck in Helix-based force-close loops immediately following their Froyo upgrades. Some have even resorted to hard resets just to get their phones back up and running.
Avoiding (or Fixing) the HelixLauncher-Froyo Mess
So if your phone is among the many currently awaiting Android 2.2 -- like the Droid X, scheduled to see Froyo in the next few weeks -- save yourself the trouble and uninstall HelixLauncher before the process begins.
If it's too late and you're reading this while stuck in a Helix-induced post-Froyo haze, don't panic. First, see if you can get to your phone's main settings menu. If you can, head into "Applications" and then select "Manage Applications." Find HelixLauncher in the list and select it. Then, find and tap the button that says "Clear defaults." That'll let you return to the stock Android launcher instead of Helix when you press your home key, which should result in your system becoming stable. Make sure you uninstall Helix as soon as things have settled down.
If your phone isn't stable enough to make it through the menus, reboot and enter Android's safe mode. The method for doing this varies slightly from device to device, but it typically involves holding down the "Menu" button while the phone boots up. This will cause your phone to start without any third-party apps running, which should allow you to go in and remove HelixLauncher from the system.
A quick note on uninstalling: HelixLauncher won't actually appear in the Android Market once your phone is running Froyo, presumably because the app hasn't been upgraded for Android 2.2 support. In order to remove it, you'll need to go into the "Manage Applications" menu within the "Applications" section of the main system settings.
So what next? There are plenty of alternative Android home screen replacements that function flawlessly with Froyo. You may even decide you don't need one, given the various UI improvements Android 2.2 delivers. Personally, I've migrated over to LauncherPro for the time being. It delivers the same functionality Helix did -- including the customizable four-icon bottom bar -- and then some.
And, most important, it actually works.