[thedevelopment]

Bookmarklets are awesome except they involve more user interaction than should be needed. I feel like almost every time I could use a bookmarklet, a plugin would do more with just as much user initiative.

They also don't have a favicon (or I haven't seen one in FF4) without a user pre-visiting a destination page, so they look unpolished.

[jschuur]

Bookmarklets are cross platform across practically any browser and work in mobile devices too. Can't say the same for plugins.

Plus it's easier for some developers to knock out a bookmarklet than a plugin, especially when you can do much of the logic server side, and potentially hook into existing code there.