yeah I throw them away. I agree Adjitator about the waste. I'm wondering why the pens aren't like the protaphane insulin pens where all you are replacing on it are the insulin and the needle and you keep the pen.... that would be less waste at least.
I store my used insulin pens and cartridges in a plastic container, my sharps in a big sharps container, and take it all to a local "Household Hazardous Waste" drop off every few months.
OM - Novolog (Novorapid) is available here in cartridges for use with Novopen and Novopen Jr. That's what I use. Unfortunately, NovoNordisk discontinued selling the Levemir cartridges in the States, so I'm stuck with the Flexpen. I hope the cartridges are still available in Canada - I vacation there every year and buy Novorapid and Levemir cartridges on my way back home.