How does the PS3 do as just a SD DVD player? I am running out of inputs on my tv and receiver, so I would like to get rid of my current DVD player, if I decide to buy the PS3.

The ps3 does very well with regular dvd's in my opinion. I don't know what d/a converters are in the ps3 but it looks to my eyes to be at least 12bit d/a conversion.
Almost as good as some up-convert dvd players.

It's good, but not as good as a up converter.

To be honest do not care about the upconverting part, as I do not have a upconverting player now. Have a Harmon/Kardon player right now. A few years old.

I have my ps3 and computer hooked to the same monitor and there is a noticeable difference in picture quality between the two. its a real shame that the ps3 doesnt upconvert, but since its not a problem for you the ps3 plays dvd's fine

To be honest do not care about the upconverting part, as I do not have a upconverting player now. Have a Harmon/Kardon player right now. A few years old.
according to people, ps3 is pretty good player with one of the recent updates (wasnt out of the box), so yes, you can replace your normal dvd player with PS3....