zumajohn,
Best of luck as you work to convince your boss to go FileMaker instead of the archaic calendar system you mentioned. The great thing about working with FMP on a Mac is that you can do all kinds of data integration using AppleScript. Depending on Now Up-to-Date's AppleScript awareness/capabilities, it's highly likely that you can use it to push and pull data between Dave's Calendar Solution and Now UTD. You may even find that you can replace Now altogether with a FMP system, with the Calendar Solution at its core.
No, I've never heard of Attain software or InControl, but that brings me to another great feature of Dave's Calendar Solution. With a Level 4 Developer license, you get unlimited access to the code, which means you can update it any time you like. This means that, as long as you have access to FileMaker Pro software, you don't have to worry about the Calendar Solution not being available in the future, since you'll be able to make modifications to the programming, and build on the solution over time.
Thanks for your post. Feel free to let me know if you have any other questions about the Calendar Solution.