Here is a link to a recent article, describing via Snowden leaks what the NSA has trouble snooping on. Be aware that the FBI amongst others has seized control of some TOR based servers and proxies during the Silkroad investigations. So take all of this with a grain of salt. IMHO if you want to send a truly unreadable message, use one time pads.
We will be bringing you lots more on digital security and other topics soon.