Some comparisons between PL191M and Dell 1800FP:
Compared 1800FP with a Planar 19 inch PL191M side by side. The PL191M does show more shadow details because of the higher contrast radio for pictures, also DVD. However, the 1800FP has noticeable faster response time, even though the specs suggest otherwise (1800FP: 30ms, PL191M: 25ms). You can see the differences by fast scrolling the text.
Regarding VGA/DIV inputs, I didn't notice much difference for the 1800FP between VGA/DVI inputs. However, there is a big difference for the PL191M (the text looks much better when using DVI). This may suggest the quality of the A/D converter of the VGA input on the PL191M is not good. Also if the video card has a high quality low noise D/A on the VGA output, DVI may not be absolutely necessary for 1800FP.
Also as others have suggested, cleartype looks not very good on the 1800FP, but much better on PL191M. In generally, text looks better on PL191M when using DVI.