Iritis is a pretty common extraintestinal manifestation of UC. According to wikipedia it's 1-3% (that's common compared to some others!)
Personally I have very very mild psoriasis and eczema in addition to UC. My UC originally presented with bizarre skin issues several years before I was diagnosed, but those haven't recurred, knockwood.
I know someone with both Crohn's and MS, too.
dx'ed UC pancolitis 5/12
past meds: asacol hd, VSL#3, apriso, rowasa, xifaxan, 6mp, cortifoam, pentasa, cimzia, canasa, butyrate, flagyl, cipro, prednisone, remicade, methotrexate, cholestyramine, cortenema
current meds: none!
step one: colectomy, end ileo 1/16/13
step two: j-pouch construction, loop ileo 5/1/13
step three: takedown 7/31/13