Go get them right now from http://developer.windowsphone.com or the Microsoft Windows Download site! There are LOTS AND LOTS of improvements in the Beta bits, so make sure you give them a try. Be prepared that there are also some breaking changes, but nothing that should take you very long to update. Also, for those of you without Expression Studio 4 installed, the Beta release also includes a copy of Expression Blend for Windows Phone 7 included in the installation.
One single download for one simple installation! Doesn’t get any better than this Just make sure you uninstall your old tools before installing the new ones according to the installation instructions.