Same experience as Rumby. I attended a Summer camp run by the Episcopal dioceses two or three times as a lad. Typical Summer camp, with almost no religion thrown in. Brief chapel service each morning, longer one on Sundays, quick prayer at meal time. That's about it. I stopped attending before I was old enough to really enjoy it (the girls, that is), but I recall it being an alright time. Really, the only thing that makes it a church camp is that the participants tend to all come from the same denomination.
And like he said, since it's subsidized by the church, it's quite affordable, which makes it an economical way to unload your kids onto somebody else for a week or two.