There are 2 kinds of receivers with video inputs.... 1 that upscale(processing to a higher resolution) as the people here are talking about, and the other just switches (usually upconverts from svideo or component to HDMI output....
With the Switching receiver, you can then run all your video into the receiver and 1 cable out to your TV by just changing inputs on the receiver... It will also pass through 1080p signal if need be, but those are not perfect either, and can introduce artifacts into the picture... not always, but sometimes.
I prefer the later (switching), it also lets you possibly eliminate a remote control.
I personally feel with all the info out there about even all the latest upscaling chips in this generation are still not the greatest, good but not great, and alot of people have had problems.
Just for example, I am using a Pioneer Elite VSX-81 and will be buying a Elite VSX-91 this years model for my next setup.. both of these just switch. I have no problems with the video passing through, and upconverting, both work great for my purposes...