<< since we're on CS,
what objects can people shoot through & with what guns? >>
All wooden objects can be penetrated (boxes on de_dust). Most "walls" (house in cs_militia) can be shot through. Things that are difficult to penetrate are rocks (de_prodigy, cs_militia).
The weapons that can penetrate are all rifles, the desert eagle, the para. The MP5 and UMP have very minor penetrating ability, but very minor (you can shoot say a corner, but not directly through an object).
vash