I've seen dirtier, but only once...and I slapped the bugger for trying to smoke out of it. Turns out he didn't know he COULD clean glass...he was taught to scrape the inside with a knife and collect the resin. He figured since he couldn't get the knife in the end of the pipe, why bother?

Yeah, glass pipes can have screens...if you get a glass screen, go for it and have fun. But a metal screen can cause problems...I find that once the pipe has been used a few times, there will be enough buildup inside the bowl that the screen will stay in. Press it down with the butt-end of a lighter, or a pen cap (something that won't poke through the screen)

Be careful though, if its pressed too far down, it'll expand when it gets hot. and since there's no room for it to expand sidewise, it'll expand upwards. and if it starts to do that, chances are it'll pop right out of the pipe, showering you with half-burned weed and glowing embers.