No, it's not just you -- Gmail, Google+ and a host of other Google services have gone down or otherwise broken. The company's status board doesn't show any issues, but Gmail users are seeing notices that their accounts are "temporarily unavailable." We're reaching out to Google and will let you know if there are any updates.
Update: That was quick; Gmail, Google+ and other services are gradually returning to normal. Some users are still reporting that individual services aren't working properly, however, so it may take a while before everything is up and running. Google's dashboard now shows that it's "investigating" issues with most of its services.
Update 2: Google has posted a response, stating that an internal software bug was the root of an "incorrect configuration" that resulted in the outage. The team is now focused on ferreting out the error and speeding up the recovery process.