I am curious about line conditioners.

The biggest improvment you might see is in the video. The video becomes less grainy, sharper and more "film-like" Too much conditioning and the colors in you monitor may begin to "darken" a bit. As to audio... read the posts in search...

I am amazed with my PS Audio P600 for my Pioneer HD-710 and front end equipment. Everything has more definition and placement. I did visual testing with no sound and only after a few comparisons did not want to watch without the P600. I have owned the Tice power block and others but found they were dispensible. This is what I always wished was available to the audio/videophile for years. Also using a power plant seems to let the equipment come through and not add any of it's own sonic signature to anything.

I also found the biggest improvement was in the quality of the video in every respect. I also experienced something similar to Elizabeth. For fun I connected my Vansevers Reference conditioner from my audio system to the Video system and found the colors became too vibrant, almost cartoonish.
I probably could have adjusted the settings on the TV to tone it down, but it was already perfect with the conditioner I was using (Audio Power Pack II).

PS: I recommend you get a conditioner with dedicated Digital AC inputs. The Video will perform best with digital AC conditioning from my experience.

Basically the power conditioner will "clean up your power". It will filter out the AC noise (such as RF & EMI)picked up by the giant antenna (all wire ran from the power station to your equipment) that exist in your powerline, thus your equipment gets cleaner power to work with. The end result is a lower noise floor, more of the original signal from you source to show through on your display (speakers, TV's etc.). As far as the digital outlets, what it'll do is separate the digital power from the analog power. Digital sources will emit its own digital noise back out so if the analog is plugged into the same bank as the digital, you just kind of defeated the purpose of cleaning up your power. A good power conditioner will have those problems taken care of in its design just as the digital source will as well. Just be careful, some power conditioners/surge protecters will limit your amplifier's ability to draw power at an instant notice. I hope I have clearified it a little bit for you.