I will try to reply in as direct way as possible:
1. Preparation for an unavoidable fight:
Aikido (should) teach you necessary skills for identifying aggresive behaviour and moving BEFORE a strike is initiated. e.g. Ueshiba once lept/ran across the room at someone who lifted their arms up in defence, which allowed him to execute ikkyo
2. Someone on top of you punching at your face:
Aikido (should) be teaching you that this is not the position you ever want to get in to; by way of fight avoidance & body movement. Aikido (should) be teaching you to limit the potential for other people to find weaknesses in your stance and techniques so you cannot be thrown or struck in potentially dangerous areas.
If you are in this position, aikido works with hip movement, unbalancing (think of kokyu ho) and wrist locks, all of which can be employed to get rid of an attacker (as I have used myself).
Combinations are hard to fight from whatever martial art (or sport) you practise. As mentioned in 1 - a major concept of aikido is to get in first. Another aspect is irimi (entering) where you get close enough (either in front or behind your partner) to avoid damaging techniques, and give you the opportunity to do technique. Unlike sports, Aikido is not about scoring points from punches. Glancing punches are unavoidable whatever martial art you practise. Aikido, being a martial art, trains you to protect your life. It derives from many potentially lethal (or at least bone breaking) techniques which were used to kill and disable, not to show off.
I have used aikido both in multiple attack and one on one real situations and have absolutely no doubt of its use as a self defence. In these case I did suffer hits from my opponents which caused bruises (boo hoo), however I put my opponents in a position where I could have killed or broken their wrists/arms (though of course I did not).
Ueshiba was regularly challenged by martial artists in the top of their field, and defeated them (And at one time crippled a judo person so he could never train again - which I'm sure he regretted). He also gained a prestigous martial arts award from the Japanese government, which only a handful of people have ever got. Admittedly he had himself trained in around 30 different martial arts, and I always encourage people who do aikido to train in is as many other things as they can - however, aikido is the framework of body movement and the philosophy in which all my training fits in to.
Aikido takes much longer to train in than most other martial arts because it is not about the techniques that you see, it is about subtleties of body movement and aspects of the technique that you don't fully understand until many years of training (and I have only been doing it for 12 years).
I write this, not so much for you, but for anyone who is interested in long term diligent training, and may be discouraged by your criticisms. I am glad you raised these points because it helps us to make sure that our martial art is based in reality and highlights the point that during training we must train as if our uke has the ability ot kill us. If aikido doesn't hit the spot for you right now, follow your own path. You have one of the few qualities lacking in many martial artisits and which was prized by Ueshiba,
[Edited by ian on November 29, 2000 at 09:27am]