The words you don't want to see if you own a Canon: "ERR 99"
My 300D blinked them this afternoon. The manual suggested removing and replacing the battery. Nope. "ERR 99" again. Switched CF cards. ERR 99. Eventually, I gently lifted the mirror to look at the shutter.
Two blades seem to have collided, rather than traveled past one another. One buckled, ripped in a way that I don't think you could do deliberately. The torn corner sticks a half-centimeter forward, straight out from the back of the body. This shutter has had it. Tomorrow I'll call Canon to inquire about a repair (most likely a complete shutter replacement, I'd guess), but I'm not particularly hopeful.
In a bit of pique I ran out and bought an old Elan 7E as a standin-in backup body that will still take my Canon lenses as you might expect these days, it went dirt-cheap. Depending on the repairability of the 300D, I may be in the market for another DSLR or two :/
In the mean time, lots of fun stand-developing Tri-X and HP5. Stand-developed 35mm Tri-X @ ISO 2400 looks pretty darned good, for what it is.