I have been using MtGox since 2011. I have developed several clients for MtGox in several languages over the past two years, one publicly available
https://github.com/qsnjason/goxsocketjs which we use for the world's only publicly available browser-based low-latency automated quant trading application
https://chrome.google.com/webstore/detail/qsn-risk-manager/mglbmemgcelnflklejcakacecblddgga. One of the principal reasons for choosing MtGox as a platform for trading was that unlike most exchanges, MtGox offers a websocket-based streaming service, making applications like ours and many others possible.
Two days and some change ago, MtGox disabled their Websocket service and forced all customers to use the REST-based PubNub platform.
At QSN, we have been attempting to bridge the gap between available trading tools and the needs of serious traders in the real world. This is no easy task. The MtGox API (v1 or v2) is a poor representation of a trading system API (I personally have worked with SETS, OPRA, NeoNet, and others). However, the crucial distinction between MtGox and other exchanges is the streaming API they provide, which provides the closest representation to an actual trading system employed in the real world.
This latest move has seriously upset us and others who utilize MtGox's platform for Market Data and Trading. We have provided a large amount of funding to MtGox in the form of trading fees and we have been ignored (my support ticket was never responded to).
This morning around 1:30AM UTC, MtGox re-enabled the Websocket service, and once again our clients appear to work.
If anyone from MtGox reads this, I urge you to consider the needs of serious traders before you embark on another regression such as the forced move to PubNub. We will not follow you next time. Also, to all you startup exchanges out there, pretending your little LAMP stack just-like-the-others "exchange" is anything of the sort, you will fail - the first guy who comes along with a proper exchange featuring things like streaming data will win - not you.