hhmmm, I've also noticed this. It only seems to happen (for me at least) when writing a mail in 'HTML' mail format - if you run 'Task Manager' at the same time, you'll see that your CPU usage goes up to 100% whenever you're typing. It doesn't happen if you write mails in plain text or rich text (RTF) formats.
I can't offer a solution, unfortunately - you could just write mails in rich text, but I guess that would mean that your recipients would only see your formatting if they are also using one of Mr Gates' mail products (Netscape mail doesn't seem to know how to display rich text, for example...).
A cynic might cry 'conspiracy' but I tend to think it's probably just shoddy, inefficient coding in the HTML renderer built in to Outlook...
cbl.