Multisite - or is there a better way?

Hi,

Before I start doing a ton of work on my website, I'm hoping you can provide me some general guidance.

Essentially what I'm looking to do is create a social network that has separate chapters by city/metro area.

Essentially, I would love if a user could sign up, pay for membership, and create their profile including choosing a city. Ideally when a user chooses their city, they will only be able to see that city's groups, forums, members, etc. It was suggested that I use multisite for this, and have a separate site for each city. Is that the best way to go about this? In a perfect world I would love for the user to be able to change their city and then see all the content for their new city without having to re-register. What I am envisioning is similar to the way Groupon works, where I can see deals in my current city but if I'm traveling I have the option of viewing deals in another city. I'm not sure that's all feasible with buddypress and groups/forums though. If you could give me some direction as to whether or not I need to use multisite for this, it would be awesome! I've used wordpress for a bunch of small biz sites but I'm a total newbie to buddypress and multisite.

Thanks!!!
Cari