There are things that I am beginning to realize about the RPi. and I have noticed a number of comments about it being a multitasking system not suitable for real time applications.
This is true. Linux is not a real-time OS. It is, however, still fast. Many people like to spew the warning without reminding new users of the actual definition of "real-time operating system." What this really means is that it cannot GUARANTEE a particular response time. While you can be "pretty sure" that it will get back to your thread within some number of miliseconds of when you expect it to, there is no guarantee, because as people have mentioned, it may have just started a garbage collection or RAM refresh routine which may take a little longer than normal. Or there may be another user process that is heavily using system resources, and isn't being "nice" about it. Alternately, something like an Arduino doesn't have the OS overhead that Linux has, so it might be able to make a guarantee like that (truthfully, I don't know. I'm not an Arduino expert.)
However, on the other hand, most applications that people claim require "real-time" processing, such as video processing or piloting a quadcopter, can actually handle late or missing data much better than the people complaining about "not a real-time OS" think. Now, if you're using Linux to directly control the precise timings of the spark plugs in an engine, that's a terrible idea. You need much finer precision for that. But for keeping a quad-copter stable in the air, no problem... If you drop some data or it comes in late, you'll just make up for it with the next update. If you miss a frame in processing a video, you just move on to the next frame, and no human watching will ever know the difference, so long as it's not happening continually. However, in either case you have to be able to handle the missing data in your software. If a developer is too lazy to build in proper data sanitization that can handle things like missing data, even a real-time OS won't keep everything perfect.