I now spend most of the time in Asia and have a Slingbox + dedicated Comcast DVR at home in MA. It's a lot better than nothing, but the picture quality really is dependent on end-to-end bandwidth.
I presently am limited to 384K upload bandwidth from my MA home, which translates into a maximum observed bandwidth at the receiving end of about 360K. When the end-to-end connection achieves that speed, I'm happy, as I can watch the games, but even then you can barely make out uniform numbers on the standard panned-out view that the broadcasters use at the snap. You'll not confuse it with a regular TV signal, and it's not worth watching it full screen, but it's no worse than watching the game in a sports bar with a smaller television.
Unfortunately, I sometimes can't achieve that end-to-end bandwidth. It's still watchable down to 100K or so, but you have to really want to watch the game to accept that, and at that bandwidth sometimes it loses sync and skips 10 seconds or so.
One very nice feature of my Slingbox setup is that I have a dedicated Comcast DVR/cable box for the Slingbox, so I always record the games whether I'm watching live or not. That helps both with timeshifting (4PM games ar 4AM games here) and just as importantly, allows me to if necessary rewatch the game when Internet bandwidth conditions are optimal.
All in all, I'm very happy with the setup because otherwise I would see no games at all -- American football is not popular at all in Asia; the World Series is broadcast here but not the Super Bowl, for example -- and it's not terribly costly. Theres'no recurring fee for the SlingBox, but I do pay $10/mo (I think) for the extra cable feed in my MA home. You don't *need* a dedicated cable feed or DVR, but I highly recommend it if there's any contention for the TV with the folks back home.
But it's not a real substitute for a real TV feed, as the quality is much lower.
Within the home, the Slingbox can use full LAN bandwidth, and the quality is excellent, with the following caveats; it doesn't support HD, the cable box it's connected to cannot be outputting an HD signal to any TV it's also connected to, and only 1 SlingBox session at a time is permitted (in addition to any ordinary TV sessions via the same or different cable boxes in the house). But it's a nice feature if you want to watch the game (or anything else!) while surfing in the study.
The Slingbox window can be sized from tiny to fullscreen or anything in between, and you have full control over the cable box remotely.
They also have a PocketPC client, but not yet Palm, Mac, or Linux clients.
I mentioned cableboxes many times above, but the SlingBox will work with just about any home TV setup, including DirecTV.
Also note that the NFL is offering (via Yahoo) an Internet GamePass feed to customers outside the US (only) for $249/year:
http://sports.yahoo.com/nflgamepass
I've only tried the demo a few times, and it's had variable quality. At it's best somehwat better than my best SlingBox quality, at it's worst unwatchable. The only save games for a week, and of course you can't watch any other TV programming. The Slingbox offers all programming available on your home TV.
Hope this was helpful.