I take your point that Ofoto, etc have been around for longer, but I haven't seen a photo sharing service that matches Flickr in terms of building community and the process of actually sharing pictures. On every other site I've ever tried, you only get to browse one person's pictures at a time.
On Flickr, the emphasis is on exploration and it is made very easy to share your own photos, and browse other people's.
I know other sites have similar features, but I think Flickr's implementation of them is better.
I'd say a professional photographer could do well simply by posting a handful of photos there, just to establish a presence and join the community. There's no need to post every one of 40,000; just your favorites.
You're right about prints, though. That's something I'd expect them to offer very soon, especially now they have the financial might of Yahoo! behind them.