The Google Webmaster Tools "external links" report is buggy over the weekend. The tool is not showing any backlinks anymore for, I believe, any site.
For example, here are the non-existent backlinks for the Search Engine Roundtable:
The issue started Sunday morning or early afternoon and is still an issue at the time I write this. Hopefully it will be fixed shortly.
Now Fixed: At about 3pm (EST), it has now been fixed. JohnMu, a Google Webmaster Trends Analysts posted below and I confirmed it is now fixed.