We did this for our app, quplo, which is still in public beta as we figure out payment (like these guys describe). Our app involves some complicated javascript for a syntax highlighted, code completion-supporting HTML editor. Common sense indicated it wouldn't be a good idea to invest lots of time making things work in IE when a) Analytics showed less than 2% IE visitors, b) our target audience is web designers and developers who by and large don't use IE as their preferred browser, and c) the app is an enclosed environment where it's okay to say "use these browsers for the app".<p>So what to take away from this? If you're a startup, you should be prioritising, not obsessing. And high on the list is making money, not making a marginal number of users happy, handling politics, or premature optimisation (eg. writing code that works across all browsers).<p>One thing we messed up on: not creating a kick-ass UX on Mac from day 1. We fixed it in the meantime, but we're developers using Windows, and a significant portion of our userbase is designers on Macs. So Safari, Firefox, Chrome and especially things like Mac font rendering and UI controls needed to be lickety-split.