I just signed up for MobileMe and bought the family pack — when I activated the account, though, it looked like I had an “individual” subscription, not a “family” subscription.
Their terminology is pretty confusing to the casual observer.
If you buy a “Family Pack”, you’re really buying one “individual” account as well as four “family” accounts. The account that you activate MobileMe with will be the “individual” account that has the 20GB of storage (so choose the username carefully).
To activate the family accounts, first click the account tab (the far right
button), then click “Account Options.” You’ll see this:

There’s several scary red things saying stuff is going to expire, and credit card billing information missing. You’re supposed to intuit that the tiny “(Set Up Account…)” link is what you’re supposed to click to add your 4 family accounts:

This experience was not pleasant. Nebulous terminology mixed with user experience mistakes will cost Apple a lot of support calls and emails.
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