Have you ever seen a solution for the mailto: that opens Outlook Express when you want Gmail etc.?

I’m wondering if I should devote time and resources to building a solution I’ve named MailToPro that will detect mailto: links on any given page and when those links are clicked there will be a popup that will allow the user to effectively start the app on his computer or else redirect to Gmail, Hotmail, etc. — do you know of anything like this, or will I be bringing a good solution to market if I develop it? Thanks for any feedback.