Although I've never been in any fights with someone who seems to be really good at martial arts (probably a good reflection on martial artisits as a whole), I've never been in a fight where I've ended up being on the ground. (I was thrown once, but they threw me away and my reverse ukemi had me on my feet in no time).
A few questions really; do fights end up on the floor? and has anyone been the victim of a particularly good martial artist? And, if so, did that make a big difference in your response?
I can believe that many fights end up on the floor. But its probably due to the guys involved not being very skilled. There is no clean takedown or sacrifice throw, just them tripping over their feet.
Take downs and sutemi (sacrifice throws)are very effective if executed correctly. Their main use is in situations where you are against a bigger, stronger opponent where conventional throws don't work. This isn't ground fighting but where you are using your weight to break joints, slam or choke someone out.
Its a good idea to test your aikido against other styles. Just do some friendly sparring with your mates or have a look at some other schools. Probably the safest way to prepare...
I have never been in a fight outside of a dojo. I have been confronted many times but have always been able to avioid anything by appologizing even if it wasn't my fault. Worked so far... hehehe