Here's how I see it: your software doesn't "not support IE". Your software "doesn't support IE today". You have the rest of your life to rectify this if it matters to you.
Other things may, for the moment, be higher on the priority list. That is OK. For example, if your are getting 10 visits a day, and your software does not support any printer but the default one, a non-trivial percentage of your ten visitors a day will be much happier with you if you fix that. However, for the moment, you'll have better business results if you work on your SEO to get to 100 visits a day, and tell anyone who complains that you're sorry and that a fix is in the pipeline.
My software really didn't support any printer but the default one, for about two months in summer of 2006. I am probably the only person alive who remembers this, because customers have more important things to do with their lives than remember and remark upon software that didn't meet their needs.
My friends who strongly advise against launching "half-functional" software like this say "But but but you'll poison your brand image with everybody who gets bitten by it!" First, if you actually manage to establish a brand image to poison you're far ahead of the game. Second, it isn't "half-functional", it is "fully functional for the set of functionality implemented right now". The people who just print to their default printer don't perceive it as damaged. Similarly, IE support should almost certainly be on your roadmap, but if it doesn't work today that doesn't mean your Firefox users will curse your name.
1. Customer Development
2. Product Discovery