I personally have never ran into this problem, but a friend of mine just did and found a very nice solution which is worth sharing. The launcher on his Verizon Samsung Fascinate (a variant of Samsung Galaxy S) went into a permanent Force Close loop, which means that the launcher would crash every few seconds not allowing to launch any apps, including settings. The displayed error message: “The process com.sec.android.app.twlauncher has stopped unexpectedly. Please try again.” Rebooting and removing the battery did not help.
In this case, however, notifications did work. The solution was to go to market.android.com in the computer’s browser and install a 3rd party launcher to the phone (ADW.Launcher in this case; LauncherPro is another popular option). He was then able to pull down notifications on the phone and start ADW.Launcher and forget about the stock launcher.
Not only did this solve a problem of the stock launcher being stuck in the Force Close loop, but he is now enjoying multiple advantages of the ADW.Launcher and wondering why he didn’t try it earlier. For few examples of the ADW.Launcher niceties see this post.