AJAX Error Arrow

I hope to have the opportunity to see if I can make some long, ugly forms (Blogger Settings pages, anyone?) verify and submit with XMLHttpRequest. Some thoughts:

• onblur validation would be really neat. It could even call back to the server to check on constraints beyond mere formatting (for example, “is this BlogSpot URL taken?”), or even do everything server-side to prevent the duplication of effort intrinsic in JavaScript validation. When the user pauses, go back to the server and check and, if there’s a problem, the little error triangle could pop up to indicate and explain what’s wrong.
• In the case of an error after the user clicks “Save,” have a nice looking arrow pointing towards the error explanation, possibly as a prelude to auto-scrolling. It could fade in quickly and serve as an indication that we’re about to scroll the browser window to the location of the problem.