Apple's software does basically everything that Entourage, etc do, but it all ties in together much better. For instance, I use Mail for all my personal email (for multiple accounts), which gets it's information from Address Book, and i use iCal for all of my personal/work/social activities, which can interact with Addressbook (for invitations, etc), and at the end of the day, all of my contacts and schedule info are downloaded to my iPod and soon-to-be cellphone... And the best part is, I don't have to think about any of it...
I love it, and i don't even have .mac. But the tie-ins just keep getting better from there... Basically what i'm saying is whether or not you buy .mac, switch to Apple's software... It's a treat to use.
pnw