Thank you for the responses. I would have to go through them later in the day when I have more time but am happy to see healthy discussion here!
I just thought that I'll chip in here what I tried in my dojo yesterday night.
One of our seniors showed me that udekimenage executed in such a way that really propels you forward despite the attempt to post.
What we did was the following:
a) Uke is offbalanced to the side (he's slightly leaning off where his extended hand is). I knew this but it was the 2nd bit that really made the difference
b) A twist in the extended hand
has to be be applied firmly (if you're nage, you are twisting the hand TOWARDS YOU, almost but not exactly like a motorcycle rev I suppose). This helps greatly in twisting the opponent's body into a more off-balanced position and generates a bit of 'lift' where the uke feels like he has to tiptoe a bit (similar to the action on the wrist on a shihonage entry). I felt that the twist and lift were key in off-balancing the uke in two more different axises.
c) Then drive forward and down with the shoulder (of course using your whole body weight) against the upper arm just above the elbow. Uke's arm should be brought close to you while you do this so that nage's full weight is felt into the throw and not just an attack on the elbow.
Even from a static position and WITHOUT the leg post (though I suppose no harm to implement it as well), uke is flung to the ground and attempts to post made him almost eat his own knee. Uke was significantly larger than me but for the sake of practice and theory we started from the offbalanced position and then he resisted.
One of my main problems was that my wrists are comparatively small and frail in comparison to my size so having the required wrist strength to achieve this twist was difficult especially against people with big or strong wrists. Having strong wrists you have to admit helps a great deal both in taking techniques and also applying techniques. Indeed in Aikido we have exercises to strengthen the wrist so I guess time to do more of those :P
Just to clarify that the 'boxer thing' is a separate issue from the 'udekimenage' question. It just developed and somehow got merged until I myself got confused as to what my question was Until Demetrio and Joe's discussion I was not asking how to apply udekimenage to a boxer's punches.
The main question is: How to apply udekimenage against resistance where many ppl have contributed here and I believe I might have found the answer as above.
The second question which branched off (and then unwittingly merged) was: When facing someone who punches reasonably well (i'm not even talking about a trained boxer which Aikido is not designed to deal with and I GET THAT (lol so please don't say square peg round hole thing) ) but perhaps your average Joe who knows how to throw a one-two what kind of strategies and techniques are effective. I posted what I felt worked for me (and a video albeit a poor example of it) but wanted your thoughts. You have to admit that in a 'real life' unarmed situation, punches are by far the MOST common and they aren't of the sort that we practice in dojos.
So let's separate the two questions now since it is clear that udekimenage ISN'T an ideal technique for one-twos or balanced strikers.
I can say this having got into several altercations myself from idiots who just wish to pick a fight (for e.g. jealous ex boyfriends or guys in clubs trying to show their stuff). In those situations, no beautiful Aikido technique flowed unfortunately but just a step off the attack, followed by a punch to their face which was in my EXTREMELY FORTUNATE cases sufficient in flooring them before I quickly left the scene.
An interesting story which I wish to share, one of these guys even had the cheek (after I had floored him), to ask me to give him a free punch back since I had 'punched him first' (he attacked first but I made contact first) and grabbed my belongings (my Blackberry with all my contacts and business e-mails) refusing to let me leave. After about 5 minutes of trying to get my stuff back through negotiation or quick snatches, I unfortunately just lost it, high mounted him and then threatened to end him after which I think he was shocked at my change of demeanor and started shivering maybe in fear or god knows what.
I grabbed my phone then left but I was not proud of myself that day as I knew that if he had attempted to punch me while I was in mount, I would have just gone berserk since I was so close to the breaking point. Would have been nice to get him in some nice Aiki lock and then retrieve my Blackberry rather than losing it that day but looking back I really wouldn't know how else to have dealt with it.