In an effort to save anyone who might read this a couple hours of frustration in their life, I wanted to share my most recent experience. I had some background graphics on a couple of divs that were working in Firefox, but not in IE. It was getting the best of me because I could not figure out what was hapenning. Now, I did have another element here that was positioned fairly strangely, so knowing that IE doesn't like that sometimes, I decided to restructure it. I spent about an hour or adjusting the HTML and tweaking the CSS accordingly. I then refreshed the page to find... no change. Perplexed, I dug into the IE Developer Toolbar and noticed that it wasn't even recognizing the graphics, as if they didn't exist. Finally, inpsecting my css a little closer, I found this...

background: url(http...)0% 0% no-repeat;

Are you kidding me?  )0%  ... I didn't have a space!

Firefox was intelligent enough to figure it out, but not IE. So I spent an hour or more trying to fix something that should have taken about 15 seconds.

Lessons learned today?  Always check (and double check) your syntax!