Funny story a couple days ago on the Change Marketing blog about a group of local high school graduates who chartered an OC Transpo hybrid bus--the red and white limousine--to get to their prom at the end of the school year. And, with the cost spread out over the 25 or so riders, it only worked out to about $12 per person--cheaper, and better for the environment than your conventional limousine.
Charter services is one of a few non-standard revenue generators for OC Transpo. Not sure what percentage of their actual income is resultant from it (I'd wager it's a small percentage), but occasionally you'll come across these types of things--people chartering a bus for a wedding, or a prom, or any other special events. Good for the travellers, good for the environment, and good for public transit? Fine by me.