A lot of people experienced a brief period of downtime for Gmail today. Personally, I tried it once and got an error, and then was able to access a minute later. A lot of people were talking about it on Twitter, as well.
At 12:30 PM, Google updated the Google Apps Status Dashboard to say:
We're investigating reports of an issue with Google Mail. We will provide more information shortly.
By 1:10 PM, Google updated it again:
The problem with Google Mail should be resolved. We apologize for the inconvenience and thank you for your patience and continued support. Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better.
There was a similar pair of updates on December 6th as well, but much later in the day, at 7:59 PM and 9:36 PM.
Prior to that, no issues are observed on the dashboard for as far back as the beginning of November. There was an outage for a number of Google services on Halloween, but since then, it's been pretty much smooth sailing until the past few days, but even then, the issues were quickly resolved.