I think so
I have always been using MM, but don't pay the 99$ fee. I still think it would be worth the 99$, but only if one really uses much of the functionality.
As a mac user, I really like the simple as heck integration with iphoto and idisk. I can just put photos onto the site, it is a nice look and they get sync'd up to .me and others can view, subscribe, download, etc. Even full resolution products. This is worth at LEAST 30-40$ a year. Not including the mac syncronization. If one didn't use that feature, it would be worth less. Not worthless.
I LIKE the calendar syncing, and that all my contacts are backed up in to the cloud, although it would be just as easy to sync locally.
More features are being added yearly, and I think it will be even better. Things like being able to upload videos from the 3gs, easily and even privately are great additional features.
If one ONLY used email, or maybe email and calendar, then I would say NO, it isn't worth the 99$, since would one could easily replicate this with gmail or other services like yahoo.