As I understand it, Tether was meant to be supported at a rate of $1 per Tether, with the dollars stored in Tethers vaults. Tether was meant to have regular audits to provide transparency and verification to its users. However, the last major audit was fraught with problems and the auditing firm quit without publishing any reasons as to why. Then, both Tether and its major exchange, Bitfinex were subpoenaed for suspicious activity. This made everyone nervous, as much of the crazy activity that happened over December was due to people making purchases with Tether, and if that Tether is worth nothing, then that means that the currencies are also worth nothing. However, it has been over a month and there have been no new developments, so no-one is really sure what is going on there.