Tor attempts to work around traffic analysis by using fixed-length records, and being a bridge helps hide your traffic with other people's. But nothing's perfect.
"Secure" in this context means "not readable by anyone but the recipient". Of course, if you have the recipient in custody, this is the easiest method to decrypt the messages: http://xkcd.com/538/
(OTR-style cryptography is nice, but sucks for store-and-forward communication; for a comporably difficult message to decrypt more than once, use one-time pads - but don't complain to be about distributing the pad dictionary, that's totally out of scope here ;)
"Secure" in this context means "not readable by anyone but the recipient". Of course, if you have the recipient in custody, this is the easiest method to decrypt the messages: http://xkcd.com/538/
(OTR-style cryptography is nice, but sucks for store-and-forward communication; for a comporably difficult message to decrypt more than once, use one-time pads - but don't complain to be about distributing the pad dictionary, that's totally out of scope here ;)