I have developed two simple tools for MetaTrader that you may find them useful. A Script to report Fractals values: http://www.forexbrace.com/4xbrace/forum/index.php?topic=91.0 An EA to return Bar Indexes: http://www.forexbrace.com/content/view/205/52/
Overall its a good product. There are some limitations but it's a very user-friendly platform. You can find the charts and trading tools in one place and also you are able to develop programs to ease your trading experience. As far as I know many brokers (they claim 400+) are using MetaTrader right now so it is quite popular I assume. Among them are FXCM, Gain Capital (Forex.com), Interbank FX, and many others. The main problem with MetaTrader is that it is a client based product. It means that you have install it on your machine. It makes you dependent on Internet connectivity. Somebody with poor connectivity could face many problems. I have written a short article on http://www.forexbrace.com/content/view/23/77/ that gives you a bit more info about MetaTrader. You may also see a list of MetaTrader brokers on http://www.forexbrace.com/content/view/85/77/. There are some serious rumours about a new version of MetaTrader on its way. If released it could hopefully make it very near to an ideal trading platform.
From a system/autotrader perspective, MT4 is really one of the best solutions for learning how to system trade, back test, etc. There are lots of much more expensive, much more sophisticated solutions out there, but MT4 also does just fine. Trader 5of7 @ TheCollectiveFX.com