With Safari 5 one of the most interesting new features is the support for Extensions. If you’ve ever used Firefox or Chrome you might be familiar with these.
For more details you might want to take a look at Mac OS X Tips, where these is a detailed description and links to useful Extensions.

There are not many Extensions that would be useful for chemists but I had a few ideas, so with help from Matt at Mac OS X Tips I now have the first extension available. This one allows you to select a drug or chemical name on a web page and use the extension to display the structure. You can see more and download the extension here.