Gnu as a prefix pretty much is a warning to stay away unless you're a total geek.
I'm trying two automated trading pkgs right now: NinjaTrader and Prodigio, which comes with Think or Swim. I can program the 1st in C#, and got up to speed on that one in a day. User interface is as sucky as it gets.
Prodigio has more of a user-friendly interface, and a normal person could probably use it out of the box in a half day. Me? I'm still struggling with it, but as I'm impressed with some of its features I'm going to struggle until I understand it and can test it and compare properly to NinjaTrader.
Just to show you how us geeks are...

Open source software is work in progress. You can do great things with it, provided you keep that in mind. The geeks - and others - who pimp it as finished products have little notion of quality as their only metrics are hackers metrics.

Makes me marvel all the more at guys like the Google founders or Zuckerberg, who somehow managed to understand that you had to go beyond mere programming prowess and pay very close attention to useability. They either incorporated it into the programming that they did, or had the humility to know they needed to delegate that to someone who knew all about it.
That would have been an interesting angle to The Social Network movie, instead of all the sour grapes soap opera stuff.

Facebook doesn't involve any technical prowess. Why Facebook won and not Myspace or one of the many others that competed with it? Maybe business networks? The nature of its first user base? A mixture of factors (including user orientation indeed) linked by a bit of luck, and the right business networks.

Google was heavily user oriented on top of technical prowess. There is much more genius there than in Facebook, not much room for luck.

I've had good and bad experiences with open source. I use some open source things, mostly those where by luck I suppose the team had someone who cared about rationality in the user interface, and where again probably by luck, as much attention to usability as adding yet another feature to show off Code Skills....

I suspect re any platform like Facebook, there is a usability factor that directly feeds into building network effects. I recall my first encounter with MySpace, very confusing, disorganized.... Never made me think, "Hey, I can use this." In contrast, Facebook - I forget how I got there, some friend I suppose, was on its face easy to use, and at that time seemed streamlined.

Re Gnucash, as much as I wanted to use it, it just was painful. Very poorly implemented on the user-interface with a level of arcaneness that was just irritating (even when, like the banking systems, I knew what's going on since I know about bank systems - but using something for personal finance, I don't want to labour away as if I was in Bank IT).