Oooooh hot topic or what?! Which position is most aerodynamic?! You could get your PhD with this one. I currently have mine on the downtube but it keeps getting knocked off whilst riding...the end of my long baggies catch the pump and flick it off the clips and onto the road. So far no following car has ridden over it! and it's a real pain having to retrieve it. So I'll be putting mine on the seat-tube...which got me thinking about the whole aerodynamics thing (not that it'll make any difference to my commute!) Yeah, I know 'don't wear those baggies' I hear you say...but I like them!