I guess the most popular function on Facebook would be the advertising space. With 250 million active users and advertising space still reasonably priced many businesses are using it, and effectively! Facebook has a very powerful advertising engine which allows your business to target a very specific demographic target, even giving information like how many that targeted ad will hit.
The actual Facebook page you have for your Businesses profile is very powerful Ashwell. They give you your brand or the identity on Facebook so people who like what you do or are interested in your business can become your fan. This becomes visible to that persons friends so they too are likely to look at it. You can store videos, photos, custom applications and information about your business.
Groups on Facebook are built around a group of people rather than promoting a individual business or brand.
The ‘Poll’ feature on Facebook is great for marketers looking for an answer about a particular feature they are looking to implement, or to keep the friends or fans interested in your profile as they are interacting with you on a regular basis.
The newest feature announced at F8 is Facebook Connect, this enables your site to easily integrate with Facebook easily. You can now integrate Facebook into your login process, retrieve users friend information and even post data back to users Mini Feed so all their friends can see their activity.
One of the few things I think Facebook should still look to do is for business profiles to be able to able to make ’skins’. Like twitter, YouTube… etc. you can have your own background and a lot of businesses use their logo but Facebook hasn’t quite got to this point yet. I feel that business owners should be allowed to have control over this feature but we’ll see if they do or not.