For the last decade or so, most popular websites have had a vast quantity of features. Today, it seems the opposite is gradually becoming a reality. And with good reason. So, if you have not already, prepare for simplification!
Increasingly more upcoming websites do fewer things than their competitors on purpose. By the way, I think this is great and I really think the trend will accelerate in the future.
Twitter is the obvious manifestation of this minimization/simplification trend. It does far less than its competitors and still, it experiences an enormous success: 20 million users and counting. Another example great example of this trend is the company 37signals who introduced me to the "Fewer features on purpose-dogma". They've based all of the products on the idea of intentionally offering fewer features than their competitors. Their products are very popular and the company as a whole is doing great.
As an example of how not to do things, take Facebook. I'm sick of all the redundant information that jumps in my face when popping by even though I can "hide" friends from my news stream. I am not interested in knowing what Sex and The City character my cousin would be and I really do not want to buy my friends as a pet in the Pet Society game. And quite honestly, I do not think I'm the only who feels this way. They really should remove these annoying features entirely, or at least give the user better control of what they want to see/use.
So how do these guys do this? How can they be more popular by offering fewer features? By actively choosing to offer just a few selected features, you enable yourself to optimize these features to absolute perfection. And that is what really makes the difference now. It is not how many features you offer that matters. Instead you should focus on offering the right set of features, and improve the implementation and presentation of these to absolute world class. This is what matters now.
Another movement, that favors the idea of reducing the number of features from each site, is the rising of The Semantic Web, which enhances the ability to show information across websites. With sites being able to collaborate easier, why should we all care implement a login system, a friend system, a mail system, etc.? As the semantic web grows mature, the need for implementing all these "common" features will decay, as we can just hook our system into some login/friends/mail service without compromising usability. Instead we will (should) focus on our core features instead and being world class in our specific field instead of spending time creating stuff, that already has been made by others.
If you already own a successful website I encourage you to really think carefully about simplifying your site. At Virtual Manager we have found that this strategy not only gives us more time to improve our core features, but also makes the site more appealing as well - too many features is a great way to scare off new users.