Did you modifiy any of the shortcuts in Aperture on the MBP? The shortcuts are tied to application not the library.
Also what version of Aperture is on the MBP and on the iMac? The image tool tips shortcut changed sometime around 3.2 or 3.3. Use to be just the T key to turn it on and off. Now it's ^T (control T)
You can export the custom command set from one Mac and import it into the other to get the exact same keyboard shortcuts. (Aperture->Commands->Export) from your Macbook Pro then copy that file to your iMac and (Aperture->Commands->Import)
If you only had a couple of commands that were customized it might be just as easy to just start from the default set on your iMac and customize those commands that you want.
To elaborate on what Frank said, the metadata shortcut was "T". Apple changed the default command set at some point during an update. The default for the metadata popup changed from T to ⌃T. If you are using the default command set, the command will be ⌃T. If you have a custom command set that you created prior to the Aperture update that changed the default, your shortcut will still be T.