Please post lovely large images, however, if you do, please ALSO use an LJ-cut tag, which hides however much of your entry you want from the Friends pages of all the members. This is good for two reasons: 1) some people still have dialup modems and getting large images when they don't necessarily want to is annoying and 2) it saves YOU bandwidth. Many newly posted images are broken because they are hosted on some free server that has a daily bandwidth limit. If your images are loaded every time someone checks their Friends page, you'll run that over real quick, especially if they're large images.
So use 'em. Nuff said. Practice on your own journal first if you need to.