Yeah, I don't think there'd be a lot different. Maybe there'd be less "lol!1!1"-type posts and a lot less "faux-sexism because it's so witty!"-type posts. >_>;
We'd see a lot more emoticons.
The more life-scarring yaoi would be the new porn.
Grammar nazis would be less plentiful. We ladies tend to type better (I'm generalizing) and, from what I've seen, we don't care quite as much if you put the period outside of the quotation mark...
As far as websites themselves... well, look at it this way. Women already go to their areas of interest. We blend right in really (again, generalizing). And I disagree about the wit thing... I've seen some of really witty, funny women (Nostalgia Chick, anyone?). A lot of men are just more outright or elitist about it.
But what age demographic are we talking about? That really would make a big difference too. If it's as broad as it is now, we'd see few to no changes... but we young ladies aren't always interested in the same things as the older generation, so if, say, late 20's/early 30 year olds ruled the internet, then all those child development and home arts and crafts stuff would be even more plentiful than they already are. Normal moms are late twenties/early thirties, right? I have no idea. Bad, narrow example, but hopefully ya'll see my point.