30 minutes? That's just three times the expected value...

Everything's fine - there have been incidents of no block being found for over 60 minutes so don't worry and maybe use the time to read up on some statistics.

When no block is found for half a day we should probably start getting suspicious

I'd love to see a real-time histogram of the block generation, just so it could allay fears like these. It's just variance, like other posters have said.

At least your thread got me interested to take a look at some block chain statistics - the longest time between two blocks was over 25 hours! That was back in the early months of Bitcoin but nevertheless interesting. Since about January 2010 it was relatively stable with one exception in August 2010 where I think there was some attack due to a bug in the client which had to be fixed manually. The longest interval within the stable period was on May 15th 2011 with 94 minutes!