I've had a Slingbox Pro for several years now connected to an HR21 and now to an HR24, and I use it all the time. I use the Slingplayer client for Windows, Mac, Windows Mobile 6.x, and recently purchased the Android client for my wife's Droid, which works really well. The Singbox gets a LOT of use in our household. Some examples: Watching the news on the deck in the morning while drinking my coffee; watching a different TV program in the same room as another family member (one person watching normal TV, while another watches a different program over the Slingplayer on a laptop with headphones - might sound a bit extreme, but there are times); keeping the kids entertained in the car on long trips (via one of our smartphones, or on a laptop using a 3G air card); In hotels when I travel (nothing like getting caught up on your own shows instead of channel surfing and watching commercials); on my smartphone while waiting for just about anything. And if you're a sports junkie, it's priceless. It's honestly one of the most useful gadget investments I've ever made, and the kicker is that there's no service charge - a real rarity these days. Just buy a Slingbox and use your existing home/mobile/public WiFi internet access.
If you're looking to get in cheap, you might try picking up a used Slingbox Pro off eBay or something. They seem to sell for around $100. I think that's the oldest Slingbox model that is still supported with the streaming protocols they're using now. Your resolution is limited to 480 lines with that model, but that still looks very sharp on a laptop, and matches or exceeds the landscape resolution of most smartphones today. On my laptop, I typically get a stable, watchable picture at about 200 kbps, a good picture at about 500 kbps, and a great picture starting at around 1Mbps, give or take a little. On the smartphones, the PQ is almost always great when you're in a 3G coverage area. Even in 2G/1X coverage, I can still usually stream audio, and sometimes even a low-res picture if the signal is stable.
The DirecTV HR2x DVRs will output to both HDMI and component simultaneously, so they work well with the Slingbox. Even though the Slingplayer Pro stream is limited to SD quality, using component video between the DVR and the Slingbox definitely makes for a better picture with fewer artifacts. You do need a separate dongle to support component-in on the Slingplayer Pro, so keep that in mind if you shop for one used. S-video and composite are supported without the dongle. I think some of the newer Slingplayers don't need the dongle and there is an HD model now too, but I think you'll probably only see true HD PQ when streaming locally from your LAN. Then again, with FiOS, you might be able to enjoy HD across the WAN too. I have streamed at 3Mbps+ over the WAN a few times recently (I have FiOS 20/20).
About the only compromise is that you have to leave one of your DVR remote controls in IR mode since the Slingbox uses an IR repeater to control the DVR. Now, with whole house DVR, I can remotely watch content from all four of my DVRs. Highly recommended!