by the way, i don't think it's been mentioned in this thread, but it has in others. in those other threads, we've found what may be the easiest (and most reliable) way to punch holes in cartos so far.
Shop Watts 1/4" Brass Self-Tapping Saddle Valve at Lowes.com i bought one last night and filled a couple of old cartos so full of holes that they looked like swiss cheese. It's really easy, all you do is put the carto in, tighten the screws (you can grab the threaded part sticking down with your fingers and make it tight enough, no screwdriver needed), turn the knob on the top (the thing with the T shaped handle) and the piercing needles comes down and makes a nice hole for ya. you can make the hole bigger by tightening it more after you pierce the carto. works GREAT!

just an idea, and a cheap one at that.