I have done A/B comparisons between the timeline output through the BOB and a DVD of that timeline and they look essentially identical. However, once you get past about 1.5 hours of video, there are better encoders than the Liquid 1-pass encoder that will produce better quality video. How much better is very subjective. If your video is around an hour or less, it should be excellent from the Liquid encoder.

You can also try using CBR instead of VBR and see if that looks better to you. For stuff around an hour or less, I actually prefer to use CBR encoding.