I have a 100w laser. A few things pepole need to know:
Lexan, macrolon (polycarbonate) won't cut on a CO2 laser. either a fiber or yag laser for that
40w CO2 (or even my 100w) will not cut metal, probably won't make a satifactory job of engraving as it reflects so drop some black emulsion on there first and wash it off after.
You need the proper laser MDF if you're cutting that, MDF has a fire retardant in it that prevents more than one pass
Don't cut styrene based materials without ventilation.

Love my laser, brilliant bit of kit!