I'm personally a member of a virtual airline in which Microsoft flight sim is the foundations of our hobby.
Granted there are many things that you cannot reproduce in a PC based simulator like CRM training and very spcific component failures. However you can do an awful lot with it. Microsoft flight sim is mearly the base package that you need to learn basic airmanship, using navigational aids, basic flight maneurvers and so on. However the real interesting part is when you start to buy things like add-on aircraft. The Level D 767 is replicated to extrodinary detail. So too is the PMDG series 737NG and 747-400. There are some Airbus titles out too but i've heard a lot of problems with flight dynamics and model problems. Basically they're not flying right.
Then to add to all this you can actually fly on-line and interact with Real ATC (real people I mean). Many of them are real Air traffic controllers. The procedures and terminology used are that of what is used in the real world too. Clearences, SIDs and en-route ATC is often available. Even NAT routes and clearences are replicated. Fly-in events are fun when theres over 200 aircraft flying over the pond.
Non ATC arrival routes are listed from STARs so you know what heading to fly when leaving Lambourne for example. Not everyone online adheres to this though. Ground movements try to replicate closed taxiways and aprons too. There's even some newish software that allows the ATCs to control the airport lighting. This is a big development as Red hold short bars can be activated and I imagine even 'follow the greens' maybe a common expression to be used in the near future.
In summery it can get very realistic. The software and PC power is good enough these days to have almost any systems simulated. The ability to fly on-line with other pilots also makes the experience very fulfilling. Microsoft flight simulator does make for a very good ground studies based learning tool for basic flying. You won't find much in it to help with ATPL exams but you can hone some basic skills with it.
In my experience though it is much easier to fly real aircraft than those in MFS. But for learning about certain aircraft systems in your own time it is very useful.
