Home underwent some maintenance today, starting at midnight and running for approximately 6 hours.  A notice was given shortly before the service went down for the update, and a quite a few disgruntled PS3 users expressed annoyance over the short notice. 

The service should be back up by now though, with Home v1.04 up and running.  With the new version, voice chat has been "temporarily suspended" until further notice.  No reason was given for this inconvenience, and Sony is simply suggesting text as an alternative for now:

...as part of version 1.04, the voice chat feature within PlayStation Home will be temporarily suspended. As soon as we are ready to resume the voice chat feature, we will inform you via PlayStation.com and PlayStation.Blog. In the meantime, we encourage users to make use of the Wireless Keypad for PLAYSTATION 3 or any USB or Bluetooth-enabled keyboard for text chat and also the “phone friend” features to communicate within PlayStation Home.

On the flip side, those of you who have not been able to connect to Home should have an easier time now.  The main purpose of the maintenance was apparently to "ease the difficulty some people are having," which Sony attributes to the high demand.