AFAIK, with the exception of ISE, all option spread orders are printed out to a broker on the floor, who works it manually. On the ISE, sure it accepts spreads, but in my experience it usually just waits until the bid on one side and the ask on the other equal your spread amount. i.e. it only seems to wait for someone to hit the bid/ask on both sides. you can still get lucky if someone is buying a spread one strike up or down, or getting out of the same spread you are getting into. I usually leg into it by opening the least liquid side first, and then pay up on the more liquid side. The commissions at IB can be a factor especially if you are playing the cheapo options (or even if you arent actually!). I started the paperwork to open an options acct at optionsxpress, but never got back to it.. also thinkorswim.com is fairly competitive at $3/contract. I've never used them, but I hear they allow option spreads in an IRA (the reason I was considering it).
The point about routing to the exchange you want it also very good.. if you enter a spread order, I think the whole order must be filled at the same exchange, even if one side can be price-improved at another exchange.