Donald Sensing notes that satellite-radio provider Sirius is adding television service, and says he hopes internet service isn't far behind. Unfortunately, satellite internet service is a much more complicated beast than satellite radio or television.
Most of the difficulties stem from the fact that radio and TV are one-way communication: a dish has to be pointed in the right general direction, and it catches relatively high-powered signals broadcast by a satellite from geosynchronous orbit. But for internet access you need a two-way connection, and although you typically require less bandwidth upstream than downstream you still need to send some data up -- to tell what emails and webpages to fetch, for instance.
There are satellite internet providers, and it's not that difficult to send data back up to a satellite. One such provider is StarBand, and as you can see from their price chart the initial equipment cost is pretty substantial but the monthly fees aren't too bad. The real problem with satellite internet on a mobile platform (such as a car or boat, where satellite radio is popular) is that although it's easy to receive broadcast signals from a satellite (XM Radio uses the roof of the car as a dish, for instance) it's very difficult to keep a mobile broadcast antenna pointed at the correct satellite transponder to allow for upstream communication. A satellite in geosynchronous orbit is 22,000 miles away and transponders are pretty small; it's basically impossible to keep a dish pointed properly while in motion. If your car rotates one degree your upstream signal would move more than 450 miles off target. That's why (most) satellite phones you've seen pictures of have ground-mounted base stations.
There are some alternatives, such as using a wireless phone modem for upstream communication and the satellite for download; but if you've got cell coverage then it would certainly be cheaper to use your wireless phone for upstream and downstream communication rather than bother with using a satellite at all.
If you really want satellite-based internet, there's always Iridium, a satellite phone system that uses a constellation of of 66 low-earth orbit satellites that don't need to be precisely targeted (because there's so many, and they're 1% as far away as geosynch satellites). They also offer satellite data/internet service -- at the pitiful rate of 2.4Kbps to 10Kbps (compared to 56.6Kbps modems that no one even uses anymore). In 1994, an Iridium satellite phone cost $30,000, but that fell to $1,500 by 2002. The Navy gets call time for around $1 per minute, but I expect civilians can't get that good a price, and in 1997 the cost was $6-$7 per minute. At 10Kbps it would take 3.5 minutes to load my front page, so multiply that by a few bucks per minute....
Costs will probably come down in the future, but there's a limit, largely due to the fact that we're simply running out of frequencies to transmit on. There are only so many frequencies suitable for data transmission, and they're all in use. DirecTV is having problems finding more room for their TV channels already. There's no way for satellites to carry all the internet traffic that's currently used by the internet, at any price.
(And now the caveat: I'm not an expert on this, and I'll welcome more detailed information from anyone who wants to offer it.)