Since this seems like a good place to put this, one of my little pet peeves is people not using height and width elements in their image tags. It's a little thing, it takes hardly any time to do, but can make such a difference.
If your site ever loads slowly (for whatever reason) those little elements will tell the browser how much space the image takes up (and use the correct dimensions, if you want to scale the image use an image editor), that will let the browser "reserve" the space on the screen for that image and the rest of the page can render while the slower to load image comes in.
For the most part, it's not that big of a deal but it's just such a good habit to get into. I've noticed it particularly on some of the bigger photo sites that can get busy or bogged down at times and it drives me nuts when I have to stare at a completely (or mostly) blank page until all the thumbnails load. Or the other case it drives me nuts is for banner ads when the ad service is down or slow and I have to wait for the banner ad to load (or time out) before I can read anything on the page.
It's a little thing, it won't make your site load any faster but it can make your site feel a little more responsive.