Development of WordPress moves fairly quickly and day-to-day things break as often as they are fixed. This high churn is part of our development process that aims to produce the most stable releases possible.
You can track changes on the web or through our SVN mailing list but many people choose to run the nightly builds to help us identify bugs. If you would like to be part of this process, please join the WP Testers mailing list and the nightly build location will be sent to you.
The WP Testers mailing list is the only place for support on nightly builds, please do not use the support forums or any other lists.