I got my Slingbox at the end of December, just a regular Slingbox Solo. The Pro HD was tempting, but money is tight, my primary viewing device is my iPhone, and I have a spare VCR to use for a tuner. So I chose the Solo when B&H had it for about $150 after Bing cashback. I had thought of scoring a used Slingbox one off eBay for $80-100 or so, but opted for a new model because of guaranteed iPhone compatibility and so I have a warranty if need be.
The reason I got a Slingbox is because we have several rooms in our house where I can't install cable, and I once had old TVs that could pick up a few local stations so I could have the news or the game on while I did stuff. With the new digital TV, I can't pick up any of the stations in my market on these TVs. So, iPhone + Slingbox = Always-Working Portable TV.
Anyway, I couldn't be happier with this combination. I jailbroke my iPhone 3G for the specific reason that I wanted Slingbox to work on 3G. It's fantastic and I can't recommend it more. I'm a big fan of TV in general and I am in shock that I hadn't set this up for myself before.
The software works great.Tap the icon, and your TV is on 10 seconds later. Works fantastically over 3G; I think that the quality is almost better over 3G than my Wifi.
Cons? It eats through your battery very fast. Look on eBay to purchase a spare wall charger if you think you might need one. I use my phone a lot and I think my battery may be fried otherwise, but watching Sling means my battery will only last about an hour. A seller from Hong Kong has the USB chargers for about $3 and they are good quality, I bought a couple.
Also, if you use Sling over 3G, your data use will skyrocket. I went from 1GB of usage in a month to over 4GB last month. If you are wary of raising red flags from AT&T, just keep an eye on that.
I haven't even explored the options of watching Slingbox in your web browser, etc. But yes, if you have the means, get a Slingbox. It's very neat.