I was cutting a lot of 1/8" 4" x 4" Leatherette Coasters from JDS Industries this week. The settings below were what I found on their site:

Laser Raster settings:
- 35 watt DPI 600, Speed 90%, Power 35%
- 60 watt DPI 600, Speed 100%, Power 30%

I was using a ULS VLS3.5 50 watt, and I was running DPI 600, Speed 97%, and power 32%. They came out pretty decent. Did you have the same problems with all of the files you were running? I was running strictly vector files that I created in CAD, then filled them with black in Adobe Illustrator.