Here are some examples using the rotary attachment on a glass bottle.  Scan gap was set to 0.055 for all of these (level recommended by Rabbit).  We decided that (for this particular type of glass), a speed of 350 with a power of 18 looked best.  Higher power levels increase the "fuzziness" of the graphic.

Scan Gap = 25.4/DPI, so DPI = 25.4/Scan Gap.  Theoretical limit is 1000DPI, or 0.0254

Speed: 350, Power: 15,_2 Passes
Speed: 350, Power: 18, Sample 1
Speed: 350, Power: 18, Sample 2
Speed: 350, Power: 20
Speed: 400, Power: 20

Paul -
Additionally i found that glass requires: focus above the surface of the glass, a soap and water paper towel, and
speed: 500, power 24, scan gap 0.0200
These #'s are a first pass and will be refined later.

From wikipedia: Pulsed lasercutting acrylic introduces a high internal stresses along the cut edge, which when exposed to solvents produces undesirable "stress-crazing" at the cut edge and several millimetres deep.  Annealing the PMMA sheet/parts is therefore an obligatory post-processing step when intending to chemically bond lasercut parts together. This involves heating the parts in an air circulating oven from room temperature up to 90 degrees C (at a rate of no more than 18 degrees per hour) down to room temperature (at a rate of no more than 12 degrees per hour). Temperature should be maintained as follows: One hour for 3mm thickness, two hours for up to 6mm thickness, four hours for up to 12mm thickness, and six hours for up to 20mm thickness. A rapid annealing cycle is reliable for thin sheets and involves placing them in a pre-heated oven to 80 degrees C for one hour, then removing parts from oven and allowing to cool to room temperature. .