I have an Intel Mac and the Groupcal status item is not being shown in the menu bar. When I set the preference to show the status item in the menu bar, nothing appears in the menu bar and the preference item is unchecked when I re-open the Groupcal preferences.
This is a problem created by multiple applications using different versions of MenuCracker. We've created an installer to fix this issue (25 KB download). This installer will install MenuCracker 1.4 in Universal Binary format, adjust the UI Server's plist file and require the user to log out and back in (to restart the UI Server and activate the installed MenuCracker). Note that some ".menu" products disable themselves (e.g., the wonderful MenuMeters product) and will still need to be turned back on after this fix.
Apple provides only a limited set of interfaces for non-Apple developers to create and manage ".menu" items on the right side of the Menu Bar. In fact, at one point, Apple appears to have tried to prevent such non-Apple menu items. The result is an (open source) code bundle, called MenuCracker, that helps applications place ".menu" items on the Menu Bar with capabilities equivalent to those enjoyed by Apple's ".menu" items.
When MenuCracker is used, there's an attempt to install a code bundle that can be run by OS X's UI Server when it starts. The UI Server keeps a list of code bundles, that it attempts to run when it starts, in a ~/Library/Preferences/com.apple.systemuiserver.plist file. There are many non-Apple applications, preference panels, etc. that include and use their own copy of MenuCracker.
Furthermore, there are both PowerPC and Universal Binary versions of MenuCracker that are in use. Depending upon which version of MenuCracker a product is using and which product was run first by a given user on an Intel-based Mac, MenuCracker may or may not work ... and if an application uses MenuCracker to help it "put up" a ".menu" item, that ".menu" item will not work if MenuCracker doesn't work.