Before the upgrade, .Mac offered 1GB of total storage between .Mac email and iDisk storage, so synching one's iDisk like this didn't gobble up too much space. Now that this total storage has been raised to 10GB, the tables have turned a bit for us synchers, and especially for me since about a month ago I paid for the next tier of storage (I know - I've been bit by the Apple update bug again); imagine my surprise when my iDisk instantly went from about 1.5GB in size to 19GB.
But how can we solve this problem? There are a few solutions, so you can play with these and see which fits best with the way you work.
The first solution is perhaps the more obvious: log into your .Mac account online, go to your account management page and readjust the balance of storage between .Mac mail and iDisk storage. You can knock your iDisk storage as low as you want and perhaps gradually increase it if your iDisk activity grows in the future. There's room to play there, but you get the idea.
The next solution, the one I originally opted for but have since double-backed on, is to turn synching off. You can still quickly mount your iDisk anytime you need it - assuming you're online - via the Go > iDisk > My iDisk command in the Finder (or cmd-shift-I). If you're mounting it for the first time after a fresh restart or login you'll experience a slight lag, but after that your iDisk should act almost as snappy as it did when you kept it synching. The only problem here, and the reason I'm rethinking this, is the catch with being offline: I'm not offline very often, but when I am, I still need my iDisk, so I just downsized the amount of iDisk storage I have allotted and I'm re-synching as I write this. For those who work differently however, turning off synching is still a viable option: if you're always connected or you simply don't need iDisk files both large and small always available at your fingertips, shutting off synching altogether could solve your storage issues.
The final solution I have is to simply start using your iDisk to store more stuff. After all, with a ton of extra space now you can really let loose and keep a lot more stuff in there, making it online, backed up, sharable by moving to your iDisk's Public folder and accessible via a browser on any web-connected computer in the world. That's a darn handy tool when you think about the possibilities. I'm moving more folders of documents and other files to my iDisk since it is now a pretty spacious and effortless way to store files, share them between Macs that keep my iDisk synched and back them up online all in on fell swoop.
No matter what solution you come up with, I'm not sure how much Apple can do about this considering how the iDisk seems to fundamentally work right now. It sure would be nice if the iDisk could simply expand automatically as you add files to it instead of taking a massive bite out of your hard drive, and who knows, maybe that's something we could see in the upcoming Mac OS X Leopard or beyond. For now, if your iDisk is cramping up your hard drive, it looks like you'll have to get a little creative.
thanks Mr. Gaskell