So right about Word spellcheck...if I'm bored I try to make it make pretty green and red patterns along a line, but even if I'm working I get distracted by it shouting at me. I like to do it all at the end when I've written all I want to.
The problem I've always had with Word's background spellcheck (or OE making URLs and email addresses clickable) is given the right content they suck back processing power, often redoing the same thing over & over.