The community is raving about the performance gains and other benefits of SP1. If you downloaded a European language version of SP1 though, there's a bug you may have encountered. If you choose "Air Traffic Controller" as your Role in a multiplayer session, you'll be faced with an "Aircraft Initialization Error" message and will be unable to use the Tower Controller feature in multiplayer.

We translate Flight Simulator into many languages, and in this case, part of a file got translated that shouldn't have. We apologize, and a fix is on the way! (Note that this error does not affect the English or Japanese versions of SP1.)

New non-English SP1 downloads should be posted early next week (hopefully on Monday). All you'll need to do to remedy the problem is uninstall the SP1 you installed and download and install the new one.