I tried to upgrade my site form Moodle 1.9,9 to Moodle 2.0 and even though the data conversion was successful (no errors), I could not open the site. Firefox, and IE-8 both lock up (browser not responding).
We finally discovered that it was the Glossary Auto-linking feature that was the problem. I was able to open the site in Google Chrome and I changed the Glossary Auto-linking setting to NO and the site opens in all browsers and navigates correctly.
It appears that the Java script in the Glossary Auto-linking function has a problem.