Pros
The flexibility in one's schedule is unmatched. You have no set hours as to when you need to be there or when you can leave, so if you have kids this helps out a lot. You also have the ability to work from home, and depending on how good you are at your job you may be able to work from home consistently. The pay is great if you are close with the management but, if you aren't, then the pay is simply "fair". There is free coffee, tea, and hot chocolate and they provide the utensils, plates, and bowls to employees. As I was part of the IT staff, this particular group of people are young and easy-going and everyone (for the most part) gets along with each other which makes coming to work more enjoyable. And you get to work with different technologies for the most part, just don't expect any datacenter technologies.
Cons
FXCM doesn't match on their 401k. The company has taken a horrific nose-dive recently on the NYSE. If you aren't close with management (part of the cool kids' group) then there is no room for advancement in your career, regardless of whether or not you work your tail off or how much better you are than your peers. Some people in management are less mature than they should be and tend to verbally assault their team members when they make a mistake. Overall, IT is more reactive than proactive here, so be ready. While the work schedule is flexible, your Friday nights will belong to FXCM and possibly even your Saturdays and Sundays. Being on-call is mandatory, so be prepared for numerous occasions where you wake up in the middle of the night. And if you plan to take a company phone, be prepared that you are REQUIRED to answer a text/call regardless of what is going on in your life. Management tends to think they are "bleeding edge" but they are naive and ignorant here, as I'd say they are about 5 years behind other financials when it comes to technologies and having the intelligence to implement them.