Umbraco v4 is on track and here are some dates from twitter.com/umbraco:

• RC2: Jan 16th
• RC3: Jan 23rd
• Release: 30th

I highly recommend subscribing to the Umbraco RSS feed at Codeplex to get an insight of what gets implemented / fixed:

• All Project Updates (recommended)
• Issue Tracker
• Releases
• Source Control
• Wiki

The core team usually add a comment describing the work that is checked in. As an example, here are some updates made yesterday:

• 45581: New section icons, UI tweaks, translations, sort dialog bug fixes. Reverts the "page shouldn't save if validation fails" feature..
  
  
  Here’s a screenshot of the new icons =)
• 45549: Improves en.xml ui translation, improved sorting, content picker overflow,fixed: regex form, fixed: tree padding/margins, fixed: content editor validators doesn't stop it from saving. Deletes old V2 ui graphic files.
  
  
  Click name to sort all nodes.
• 44976: Fixes 20223, Adds full Safari support for tinymce

Now, go subscribe and get involved by testing and report issues you encounter!