My problem with IGH is that if it goes wrong, which it does a few times a year for me due to gunk or ice in the cable path, it can get into a situation where I just can't find a gear that it will stay in and it's constantly grinding and catching and generally sounding like it's about to cough up a gear.

If the derailleur got gunked up, it would still work, it just wouldn't shift. I'd have to ride to work in 3rd or whatever but it worked.