During last Sunday's group ride I noticed my rear derailer was kind of bulking during upshifts in the last five of so on a ten gear cluster. It looks like it is spooling out cable as the little red ball indicator moves inboard, but the derailer shifts to the smaller cog rather slow. Any ideas?
Unhook the rearmost portion of the derailleur cable housing (the part that ends at the derailleur itself) and grease or tri-flo the cable. Dirt builds up there pretty easily and can often slow the shift down.