Think small, like 10-12KB per image. Yes, depending on the source, the number of broadband users is going up. But slow pages are still really annoying, even if you're on a T1. And huge images are a primary cause of slow pages. It's easy to optimize your images.
Web Developers Always use graphics that fit the content. Just because you have an adorable photo of your dog doesn't mean you should have it on your Web site about Web Design. The main exception I would make to this is for "design" images. These are photos or graphics that help make up the design of the page, and are not intended to illustrate the content.
Do not use images that blink or move or change or rotate or flash or do anything on your page. Or use them sparingly. There have been many studies that show that flashing graphics are distracting and annoying to people. In fact, in one focus group I watched the browsers actually physically cover up flashing graphics so that they could read the rest of the page. Stick with standard layouts. I've seen some pages that use 6 or 8 frames on one page. Another site used a layout where you had to scroll to the right to read everything on the page (but you never had to scroll down). These layouts are cute, and you might find them fun to build, but they will drive your reader’s nuts. The reason that the 3-column layout is so popular on Web sites and newspapers is because it works. You might think it's boring, but you'll keep more readers if you stick with something simple that they can understand.
Web Developers is more than the CSS property; it is a function of your layout. You should be aware of the Web Developers on your pages and how it affects how the content is viewed. Web Developers is just as important in a Web layout as it is in a paper layout. Use your graphics as elements in your layouts. Graphics can be more than just graphics when you use them as actual elements in your layouts. An extreme example is when you wrap text around an image, but any image you have on your site is a layout element and should be treated as such.