Creating upgradable bookmarklets
I haven't seen this technique before, but the implementation of Reading Blinds bookmarklet, a tool to focus your eyes on reading a page, really eases maintenance of a published bookmarklet.
Instead of embedding the JavaScript code in the link, this bookmarklet uses the DOM to add a script link the <head> of the page. This gives the developer an easy way to release improved version, just update the file and all users will automatically use the new version.