Don't forget to check your web application on other browsers!
One of my pet peeves about web designers and web application developers is the ones who don't check to make sure everything works and looks good in the major browsers, not just IE*. I am a 100% IE user at work, and at home, I use IE when I'm on my PC, but on my Mac** I use Safari.***
Recently, I've come across a couple of sites that don't properly support Safari. First, I was trying to use Zillow.com to get some prices of condos in my neighbourhood, and well, as soon as you hit it from Safari, you're denied. It says that Safari is not supported and suggests either IE or Firefox. I know many Mac users who don't have FireFox on their machine, and they don't want it on their machine. They just want to have a simple, easy to use environment.
The other site I hit, was asking for my date of birth to make sure that I was old enough**** to get the coupon. Well, sure enough, I pop in my date of birth, and it says I'm not old enough and that I must be at least 18. Ummm, last I checked, I was over 18. I'm glad it complimented me and said I don't look like I'm over 18, but still.
Yes, there is still incompatibility between browsers, and it's getting better, but it only takes a few extra hours to run a few extra tests to make sure everything works properly. If it doesn't, then do something about it. And you also learn what not to do in your next development project!
* I admit, I'm guilt of that too on my fine art web site. I know its broken, I just haven't gotten around to fixing it yet.
** Long story, but it's really only used for music, web browsing and photo editing
*** I'd use IE, but we've since cut support for it on the Mac, so I have to use Safari. I've tried Firefox and don't like it all that much.
**** It was the KFC site where you can get your free sandwich, you have to be at least 18 for some reason