Since MS will stop supporting anything before IE 8 soon, I am not sure if I should make my web app compatible with those older browsers. I know there are still people using them but I don't know if there are enough to make it worth while.
Any suggestions as to how to decide what version to support?
Thanks.
Unless it's a legacy app and needs to target IE6 users. In any case, you should not support anything below IE5. But you should try to at least look good on IE4, even if you don't have full functionality.
Or just stick with IE7+.
It depends on whether you need to make it work for as many people as possible. I can only speak for the website I've got Google Analytics on, but about 20% of the visits are IE6, another 15% are IE7. If you can afford to drop a potential 35% of your audience, go for it.
(Here's a wikipedia article on browser share, with a breakdown of IE usage. The official stats are strikingly similar to those I cited above.)
This question could provoke a bit of argument, there are a lot of people out there still avidly supporting IE6, and others like me who wish that older browsers would just magically disappear so we don't have to consider them.
Anyway, here's an answer for your question: you need to define "web app". If you mean a web application that is used by businesses in a LOB type of way, then you should be able to dictate the minimum requirements. For the web app i am currently working on, we have a minimum of IE8 or FFox 3.6. In only one case have we had a client who could not upgrade from IE6 because they were still using a critical legacy app that was built for IE6, so they use FFox for our app instead.
If your web app is going to be exposed to the wider world, and any random John Q. Public can use it, then you certainly still need to consider the numbers for each browser, and then make a decision of whether the work involved in supporting that browser is worth it for the number of people using it.
Our web app which is sold as a product to be installed on enterprise intranets suppoerts IE 7+. We dropped IE 6 recently and nobody complained thus far. Of course we also support Firefox, Safari, Opera and Chrome, but that's boring: my testing algorithm is as follows:
You should follow "progressive enhancement" -- provide the core features of the site to most if not all users; then, for the A-Grade browsers, provide the additional eye candy and features. With IE6 still being used by anywhere from 10 - 20% of web users, we can't ignore it completely.
However, we can follow the pattern of Youtube and Google: display a message telling the user to upgrade. If you go to YouTube on IE6, you can't even view any videos anymore. This is what you'll see:
And here's Google Docs on IE6:
Depends on the audience.
If you're Amazon.com, Ebay or Google, you're probably going to have to support every browser under the sun except perhaps Netscape 4.7 on Intel Solaris (Note I have actually used this combination while I did my B.Sc, but that was more than a decade ago).
If you're aiming at a broad web audience, IE7+, FF, Safari, Chrome and maybe Opera
If you're expecting users on corporate intranets, you may well have to support IE6+.
If you're aiming at mobile users, Opera and various mobile browsers.