I've hired small boats (sail & power) on Lake Annecy - good fun and not too pricey, although that was back in 2003.
For a proper laff, there's a diving board open for all foc, with 1m, 3m & 5m stages to hurl yourself off - big splash when you hit the water around 30 secs after leaving the top board.
Agree with everything EnglishLes says about the town - sweet place.
Oh and lots of campsites across the road from the lake, but they get busy, so advised to book in advance.