free unstructured data logging service?

I've been using plot.ly to plot some sensor data, but every now and then, because of upgrades or whatever, plot.ly stops working, and often I don't notice until much later.  So, is there a free web service that will log arbitrary text strings?  That way it could serve as a backup to plot.ly.  I'd just send it a text string every time I send plot.ly a datapoint.

I don't know if it's free or suitable to what you want to do, but some of our users use Thingspeak. We provided a logger that will log arbitrary data to Thinkspeak for them, and it seems to work well. You can create multiple graphs and log data to specific ones.

SparkFun has a data logging service.  I'm not sure what your needs as far as data sizes are, but it might be worth checking out: https://data.sparkfun.com/