I hooked up a PC to my TV to do so, and found that, alas, the formatting of most web pages, even those hosting lots of video, are not designed to read from that far away. You can't read menu selections or button labels or informational text.
I just use the "zoom" feature built into FireFox if/when I need to see text/buttons that are too small to read from a distance. As an added bonus, I even used a FireFox extension to add zoom in/out buttons to the main Firefox button bar, so I didn't even have to use the keyboard to zoom in/out (and can instead control zoom directly via my USB connected trackball).
NOTE: I occasionally need to grab the (USB connected) keyboard, especially when I want to do search (and therefore need to type something in). However, a lot of the time I'm just clicking on links/buttons/bookmarks/etc. And in those cases when the "mouse" (USB connected trackball) can do all the work, I often won't even bother bringing the keyboard next to me (but will instead leave the keyboard alone, and just control things with the trackball).
I admit that my setup isn't nearly has hassle free as the ROKU (which may be why I I use the ROKU a lot more often than the PC). However, that setup is functional, and seems to give access to a lot of media (web sites) the ROKU can't seem to access.
NOTE: I prefer a trackball (instead of a more traditional mouse) for controlling the video PC, as a trackball can easily be held in your hand (whereas a mouse needs some surface to walk over).
My PC setup isn't really fancy. And while virtually any "general purpose PC" it is more costly than the ROKU (and mine was no exception), my setup is still cheap by computer standards. What I did was take just about the cheapest Windows-XP netbook I could find (a really cheap and very small Acer model), upgraded its memory (to the 1.5gig max it would accept, since video playback is often sensitive to memory), and hooked it up to the LCD TV via VGA (many LCD TVs, including my cheap 32" model, have a PC/VGA input) and the stereo sound output to the TV via a cable plugged into the "headphones" jack of the laptop. I then configured the laptop to continue to run (i.e. NOT go into sleep mode) when the case was down, send it's video via the VGA jack (vs the built in display of the laptop), and controlled the laptop via a cheap keyboard and trackball (trackballs are easier to use while sitting watching TV than a mouse is) connected via "long" USB cables. I also tweaked the software settings to optimize the laptop for streaming (remove junk that you don't need to run constantly, move the Windows temp areas (often silently used for streaming video buffering) from the hard drive to a free ramdisk program, etc.).