I got rather excited about Margo's comment that you can mix Sram shifters with Shimano. I too hate the bulkiness of Shimano shifters as my short fingers cannot reach the brake levers very well from the hoods. I tried in the bike shop, Sram and campy shifters which are heaps narrower and the "blades" are flatter so my fingers won't slip. However I don't want to change my entire groupset as that would be expensive!

However I just checked with a Shimano expert I know and he said "yes you can but you also have to change out the front and rear derailleur as well".

Which kind of makes that option not so attractive...