Having all the calendars up-to-date is wonderful. I have a Mac at work, two at home and an iPod in my pocket all with the same calendar on them. That, to me, is worth the money.
There are some bonus features as well. The Safari bookmarks on the computers now match. That may not seem like a big deal, but when you no longer have to get a kid to move so you can do your research, it is.
I know I don't really need the storage space, web page and mail account because my ISP tosses that into their package, it is just nice to have a little extra. Who knows, maybe I will want a quick and dirty way to share photos when I am away from my Dreamweaver machine. Or maybe that's where the kids efforts go when they want to create web content; a kind of intro to web pages with iWeb.