Firstly, I've frequently wondered how brakes come so 'sharp' out of the box...Are there hundreds of Chinamen squeeling newly built brakes down steep hills outside the Shimano factory...?!
Anyway - I've never really 'bedded in' brakes as such. Normally popped them in and got going. never had much trouble.
However, after contaminating the pads on my new XTs, I swapped them for Superstar sintered - pads i've normally been fine with, but these were naff!
Done a few rides, never really got them up to 'heat', and they still felt contaminated.
Did a ride yesterday eve near Arundel and there were useless all the way round. The final 50m of the ride was down Arundel high street - a rather steep hill.
Pleasantly, after going at it hammer and tongs down the hill, and with 3 firm grasps of the lever, my brakes went from "so you want to stop, well, let me check my diary and see if I can fit you in..", to "getting off here sir? as you wish!"
I was so close to binning another set of pads, but a steep hill in a post end of the country has saved me a fiver......