My opinion concerning if Aikido is combat effective or not is that prior to all of this, back in Japan not so long ago, every technique was used to save lifes, or you think that when people challenged O Sensei they would throw sand in his eyes and push him or they would try to kill him? He developed Aikido facing life or death situations and we would't be here discussing this if it wasn't effective. Don't you think?
Also, for the ones that think that Aikido must be practiced with a martial spirit all the times, I do agree with you and I always try to do that, but I also see people practicing Aikido to develop a better relationship with people at work, home, etc. To get in shape, to improve their balance, attitude, to relax, and a lot of other things that Aikido can do for you.
So, when one say that it is not effective, depends on what you want from it.
Who are we to say that one should practice this or that way? Aikido is an art and as in every art each artist develops its own way to perform it.
That is the way I see it,
I hope it helps a little.