I've had a Slingbox for about 4 or 5 years. I probably have the AV version. A couple of points that others haven't mentioned explicitly.... When you set up your Sling account, you can create an admin account and a guest account. So basically, you can give out a guest password to friends and they can watch your TV--but not log in and change certain settings. With the admin account & password you can boot people off your TV at any time and change the guest account password to keep them off.
I'm not 100% positive about the more recent Slingboxes, but mine has inputs for 2 video sources--one composite and one S-Video (outdated, I know). Anyway, when I was out of the country for over 6 months, I hooked up an old camcorder to my Slingbox and was able to watch both TV and monitor my house through the camera. It worked great, and at least gave me some peace of mind.
I've had the SlingPlayer app on my iPod Touch for well over a year, and it runs great over wifi. Plus I have Dish Network and the Sling mobile software let's you log into your DVR directly too. If you don't currently have a Slingbox and are considering getting one I recommend you WAIT because Sling has recently been selling the hardware with the iPhone app included. Perhaps they'll start doing that for Android as well after they release this. I sure as hell don't want to spend 30 bucks on a Sling app.
One last feature that I don't think anyone has mentioned: if you're watching your Slingbox on your computer, it will sort of work like a DVR insofar as it will allow you to pause live TV regardless if you have a home DVR or not. It just buffers the video on your computer. I doubt such a feature is possible on cellphones given their lower storage capacity, but if you're on the fence about buying a Slingbox, it's another nice feature.