IE is still the most common browser found on the web, for some technical/IT websites Firefox is more common but on your average website its around 70% IE, 25% Firefox 5% others (Including Opera)

Realistically if you dont cater to IE you will block out more people than you let in, yes you can code for both however it does get messy. IE7 is a lot better than IE6 but from figure's I've seen only around 50% of people who can upgrade have which leaves us web designers still doing ugly hacks for IE6 for things IE 7 handles fine.

Jen