Web developers like to complain about browser x or browser y being "difficult" to work with. Bah. Sure, there are really annoying bugs in any browser, but most of the time the one you test initially in and are used to will be easy. The others will present small or big surprises. A couple of times I have written pages that only worked in Opera, because I happened to use both standardised features that are missing from Internet Explorer and IE-specific features supported by Opera but not others. A natural risk when one knows a specific browser's capabilities very well.
Here's a page I created recently that I thought was pretty standards-compliant (apart from event.offsetX and offsetY – perhaps I should ask WHAT WG to standardise those?):
..but whops, I did it again: it only appears to work in Opera. All the content is visible in any browser and I simply like creating Opera DOM capability showcases, so I won't add workarounds – but it makes me rather curious that even old Opera 7.23 does a perfect job but new FireFox 1.5 fails. I know IE doesn't get the setAttribute('style', 'some css code') part, but I have no idea where FireFox stumbles.