Most tooltips disappear as soon as you roll off the hot spot and they don't contain any links you can click. But Google has implemented some very nice tooltips on their AdWords pages that
1) contain links you can click
2) stay on for a half second after you roll off of the hot spot.
3) if when you roll off of the hot spot you roll onto the tooltip, it stays active and lets you click the link.
For example, on the AdWords Campaigns | Keyword page there is a small circled question mark by each column head that is a hot spot for a tooltip. When you roll over the question mark a tooltip comes up with a short explanation of that heading, with a link to a page with more information. You can then roll onto the tooltip message and click the link if you want more information.
Thanks for any info.