I've always had an efficacy for True Neutral characters. Whilst I haven't had the ability to pick them in our earlier D&D adventures, I've always wanted to. I'd end up getting stuck with someone CG just because the other characters wouldn't trust "someone who could change sides halfway through a battle." The rules were simple when we were kids: The neutral and evil alignments were out, which left LG and CG, and everyone wanted to be a badass with a heart of gold.
It wasn't until my bard that I finally got to try out someone TN, and I liked it. It's a character type I don't have much difficulty in roleplaying, because it's who I am. Whenever I'm concentrating and not just being agreeable (not often), I'll try and make every compliment laced with an insult and every insult laced with a compliment. I always feel awkward after I've said anything wholly good or wholly bad about something or someone. My "definitely" tends to sound like "probably", or "likely", but that's something most engineers tend to have. More than anything, I'm always aware of the advantages and disadvantages of either side, and I tend defend the one that's being beaten. Any rational side tends to have a pretty fair-enough arguement.
This is the first thing that is mistaken with TN characters: They are not fence sitters. Rather, they understand the dangers of letting either side win. They (rightly) fear that one side will become unstoppable if the other side is defeated. This stops people from questioning what is right, because there's only one choice. It's a dangerous end, and far more dangerous than an eternal struggle. The second thing is: A TN character won't change sides during a fight. If they were going to change sides, they'd rather just not fight (unless they were CN, which meant they fought for the hell of it). They'd probably try to avert a fight than fight on one side and then change sides. TN is an ethos, it's not an instantaneous test of who's winning.
The TN character is often radically misunderstood by DMs and game designers. They often see acts as good or evil, and will assign points accordingly. A TN character, to them, is one who commits an equal number of good and evil acts. It's comical to try and stay a TN character under these DMs and game designers, because they simply don't understand Neutral behaviour. Neverwinter Nights had me committing good deeds and having me kill off a few peasants every now and then to keep me from getting in the "good" alignments. There were rarely options that I wanted to pick. I could either be nice, or a prick, there was no in between. The game ended with me being CE. I just got frustrated and figured it was easier to kill everyone than be bothered with it (I was ridiculously powerful, and actually had lunch while defeating the last master, and she couldn't touch me).
The perfect counterexample is Planescape: Torment. It has an awful UI, but a great story. The nicest thing about it is that it gives me options to keep my neutrality. Sometimes even P:T is simplistic. "There are good guys, bad guys, and a neutral guy. Kill 2". A situation which demonstrates both parts of P:T is where I had to get a zombie to remember her name. I eventually clicked "Why don't you just pick a new name?" Of course, there's no escaping the rest of the conversation, so she ended up picking a new name and I ended up being NG. One load later, I agreed to try to find her name among the crypts. It was conveniently erased. Now when I said "why don't you pick a new name?", the conversation that ensued left me at TN. Hurray!
Trying to actually find her name was a neutral behaviour. It even made sense as a neutral behaviour. First... time... Ever!