Use Merge for the initial sync, it'll make your life easier.
I've had a lot of ups/downs with it in the past, mostly SMTP timeouts and iDisk errors. I still use the e-mail from time to time but it's mostly a spambucket now. A few months ago I switched to Dropbox as opposed to iDisk. The iDisk is just too
finicky for me to use reliably for an offline copy.
Syncing works really well, however, it's hardly a reason to buy MobileMe outright at $70-$99. If you have an iPhone, it's really nice at keeping your contacts/calendar/bookmarks all synchronized over the air. I've tried Google Sync and it's a close second for everything except bookmarks--not to mention free.
You've got a generous 60 days to try it out so my advice is use every single bit of it as best you can, see if you like it, and if it is worth it to you.