I've gone and done it. I've completed my first micro-transaction.
The game? Domain of Heroes.
The item? Starter pack, which gives increased inventory, an increased logout timer, a mule, guild-worthiness, chat message size increase, and extra wishes (wishes being the dual currency of DoH).
Anyone that has played or seen Domain of Heroes may be shocked that I spent money on it, but I had the $10 sitting to the side from a work-related bonus, so I wanted to treat myself.
Also, I felt comfortable supporting the development of DoH. The game is still rough around the edges, but looks to be maturing into an awesome casual web game. The developers/support folks are nice and can often be found online actually playing their own game and interacting with the playerbase. The community is also top notch.
Having played DoH for a couple weeks now, I've started to realize how narrow minded my game mechanic thought process has been during my years playing of AAA MMOGs. While DoH doesn't go too far off the beaten path, there are tons of small changes, along with the "set it and forget it" playstyle that make it refreshing to play.
All of this combined to increase my willingness to complete a micro-transaction.