I did both Sprint and Olympic (long story) this year and registered for next year Olympic too but not sure if I will go ahead, depending on the dates is going to run, as I quite fancy Scotland Coast to Coast and it may clash.
I'm signed up for the Olympic distance.
I did my first ever tri last Sunday - Sevenoaks, a sprint with extended (8k) run. Loved every moment of it, it was a real blast. Beautiful day for it, lovely route (the run is through scenic Knole Park) and excellent organisation.
I suspect London won't be as pretty but I'm really looking forward to taking part in a major sporting event. Really do need to work on my swimming technique & fitness though - I lost more time to some of the leaders on the 400m swim than I lost on the 25km bike leg! That could translate into a very big deficit indeed over 1.5km...