@guildenstern's response covers it a bit, but a bit more on why this is so important. While the nominal market cap of the cryptocurrency sector is somewhere between $500-600B these days, this is based on an estimated $10-20B of capital inflow (eg "real" dollars invested). USDT, as a de facto 1:1 USD peg acts much more like this money than another random coin, because trades into USDT are treated as dollar settled. While there are some weaknesses to some of the analysis, the recent Quantifying the Effect of Tether report [2] does a good job pointing out the correlation (if not the causation) in terms of pricing/demand.

You can also note that if you order the charts by 24h trading volume, USDT is #3 (right under BTC and ETH) [1] and if you dig into say the top 3 exchanges [3][4][5] you can see that BTC/USDT and ETH/USDT are basically in the top spots. Ignoring the Korean exchanges (who are their own little universe), you have to get down to GDAX @ #10 to get down to an exchange that doesn't directly touch Tether.

If you pay attention to the markets, you can see USDT clearly driving price movements and as long as everyone treats it as a USD equivalent, USDT drives USD prices. When new USDT is printed (easy money), then people (and potentially market manipulating bots if you are into conspiracy theories) use it to margin into BTC, increasing demand, driving the whole market up. If this is not organic demand (USDT issued due to USD deposits), then we have a huge problem, since this has been going on for months and represents a huge price distortion.

Now Tether isn't solely responsible for driving prices up - there has been a real mania (you can see it with the insane amount of signups going on for retail exchanges), with a lot of real money coming in, but there's some real dirty sausage making going on atm. A writeup that points out a lot of the messy stuff going on: https://medium.com/@Skycoinproject/state-of-the-cryptocurren...

Personally, I believe that most of the Tether is backed by real currency, however it is being driven primarily by large OTC swaps by those evading Chinese (or Korean) and potentially dark market capital controls. I don't know if this actually leaves the market any better off if/when Tether Inc and many exchanges get busted by governmental/international regulators.

These shenanigans btw hasn't gone completely unnoticed in the mainstream news. Nathaniel Popper, who covers the digital currency beat for the NYTimes has done writeups on Bitfinex/Tether [6], as has Bloomberg [7], heck, even Dr Doom is all in on beating the Tether drum now [8] although I don't think anyone is straight up talking about the likelihood of major ML going on...

Re, other stablecoins, while they'd be nice to have in theory, I think one needs to be a bit skeptical: https://prestonbyrne.com/2018/01/11/epicaricacy/

A recent insightful quote I saw was that stablecoins trade volatility risk for blow-up risk.

The most interesting stablecoin announcement I saw was MUFG's plan to release a JPY-pegged coin soon. Now that'd be interesting...

[1] https://coinmarketcap.com/currencies/volume/24-hour/

[2] http://www.tetherreport.com/

[3] https://coinmarketcap.com/exchanges/okex/

[4] https://coinmarketcap.com/exchanges/binance/

[5] https://coinmarketcap.com/exchanges/huobi/

[6] https://www.nytimes.com/2017/11/21/technology/bitcoin-bitfin...

[7] https://www.bloomberg.com/news/articles/2017-12-05/mystery-s...

[8] https://twitter.com/Nouriel