I've noticed that in iPhone's Calendar, you can't change the calendar (Home,Work, etc.) of an entry once it's been created - only at the point that it is being created. This is immensely frustrating as quite often I fail to spot which calendar an entry is being created in until after I've hit Done and I see it showing up in green or blue in my calendar. I split about 50/50 between Home and Work entries and so very often each new entry is of a different type to the last (though I fail to notice it) leaving the default calendar assignation incorrect. Grrrr.
Update: I realised that a big reason for failing to spot which calendar is being used at point of entry is that it doesn't use the calendar colour in the creation UI - only the name. If it backed the name with a big splash of colour (green for home, blue for work) I for one would be far less likely to mess up.