This is a debate that gets picked up on every bicycle forum known to man (okay, that might have been exaggerating a bit). Typically you start to ask the question when you notice that the morning after you have used your CO2 cartridge, your tyre is ridiculously low.
By no means am I a chemist but, as it has been explained to me, CO2 and butyl are more soluble than N2/O2 and butyl. Most tubes are constructed from butyl (fancy pants cyclists will sometimes use Latex tubes, haha). Due to the increased solubility you can expect that a CO2 inflated tyre will need re-inflating sooner than one you pump up by hand.
While the explanation above is dealing w/ escape from balloons I am going to assume that we can take that information and apply it to our discussion.
Now, if i am incorrect (which I often am) please let me know!
I just noticed I didn't tackle the temperature issue. I do know that temperatures exceeding 50 degrees celcius (above 125 farenheit) can result in the potential for ... explosive fun, in regards to CO2 canisters.
This company has a proprietary gas blend that won't leak from your tubes apparently ... ... ...