This plugin adds user-submission links at the bottom of each post for various social bookmarking sites.
Because I can. See http://www.tsaiberspace.net/projects/wordpress/slashdigglicious/
Maybe. Let me know what it is. In the meantime, it is actually very easy to add another site to the plugin code.
If you require something more flexible, you might consider Bookmarkify or ShareThis. The trade-off to consider is one of simplicity and speed vs. features, configurability, and possible site slowdown.
<!--slashdigglicious-->, the link icons will appear.
<!--more-->, the link icons will be turned off for non-single-post viewing modes.
<!--noslashdigglicious-->, the link icons will be suppressed.