I'm currently typing this in Opera which has the same function but unfortunately it's based on American English and flags up colour, colourised and all manner of other 'differently correct' spellings.

The one that has been getting much more noticeable as I get older is using 'their' when I mean 'there' or vice versa.

I do read things over and over before posting but somehow I just keep missing it and I used to be such a good little boy about it when I was eight years old but then I had a stern looking teacher with flexible ruler to worry about.