I went to 3 LBS and asked the same questions. The first one said no problem to change to an IRD casette with MTB derailleur. The second one talked about chain capacity and said that IRD did not shift as well as Shimano. He thought I might be able to get away with a 12-30 (not 11-30) with my short cage derailleur, but would need a long cage for the 12-32 or 11-32. The third one said that I would need a long cage derailleur for the 12-30 and a MTB derailleur for the 12-32, but that it would not shift as well as now. Apparently, the spacing is slightly different than Shimano to avoid patent infringement. He recommended learning to stand up while pedaling uphill instead (which I have not mastered yet). How do you start that? Eventually Shimano will make a 10 speed MTB cassette (2011). The SRAM one would work, but it costs $330 and is 11-34 (which I don't need). I just emailed IRD and will see what they say. It never occurred to me when I bought the bike that I could not just simply get a larger cassette.