I'm pretty sure I figured out what was causing it.

I tend to email a ton of articles from Google Reader to my wife, and I think Google was seeing this as spam. On days when I don't send more than 4 or 5 articles to her, I don't get this error. When I send about 20 in a day, I start getting it.

Frankly, if this is the case, then that's stupid. If Google is smart enough to detect that and block me, they should also be smart enough to know that I'm sending 20 things to a person with the same last name as me, through a 5 year old Google account. Besides, that has to be the most inefficient method of spamming I've ever heard of.

Anyway, this appears to be the case for me. I have no idea why it would happen in the translator.

From what I was able to research about this, it looks like people are getting it more and more frequently, but Google is silent about why it happens.