On the whole, I like the idea (particularly getting newbies out of prison quickly). Although I have a couple of thoughts:
The longer prison times could be awfully hard on priest characters since they can be arrested pretty much at will if you're that way inclined. They could spend more time in prison than out of it.
It's becoming harder and harder to find players who are interested in taking on military positions (maybe one or two players for some realms). Keeping those key players in prision for 15 to 30 days would effectively end some wars or destroy some small-to-medium sized realms. I don't think there's any power on earth that would persuade some judges to release key characters if keeping them in prison for the full stretch helped them win a war.
Maybe it would also encourage people to pile resources into family gold to have the option for the family to pay the ransom.
