I had to implement a bubble tooltip helper for a client. After a short research I tried the Coda Popup Bubbles.  Useful plugins that worked great for a couple of days, when I set it for a single text field and 2 browsers only. When I decided to integrate it as a platform independent snippet and add it to 10 more textfields, I hit a rock - indents from bubble to the textfield were not consistent, bubble was popping over the textfield etc. Some images were also missing - left and right borders in Firefox and the bottom arrow in Internet Explorer.

I used to hack the Javascript and CSS for 3 days and finally got stuck. I found a workaround working since then - the BubbleTip plugin, which is a modification of the upper one, but acting better in different browsers. Also, it's using an automatic offset which makes it far more useful when you have different text in bubbles.