This plugin is based on Youtube Brackets plugin by Robert Buzink (which is, in turn, based on Quicktime posting plugin by Shawn Van Every), and works in the same way.
WordPress.com doesn’t allow embedding Slideshare code directly, but using a bracket-based syntax is permitted. Here you are an example:
If you have migrated your blog from WordPress.com to a standalone WordPress.org based one, and your posts are likely to have embedded Slideshare presentations, this plugin may be helpful 🙂
Download Slideshare Brackets 1.0.