120hz monitors are wonderful, but it really is up to you if you want it. Try to get some viewing time at a store, or a friend who owns one. I personally love the 120hz look and feel, but my wife finds it very disconcerting, often suffering severe eyestrain within a few minutes.
So i didn't bother getting one, but really wanted to, heh. Figured I would save some cash since it would be running at 60hz half the time anyhow.
There is also the arguement that interpolation (the process that creates the extra frames should you be supplying it with less than a 120hz signal) creates visual lag, and can also be a detriment to gaming. Though I have yet to experience this phenomenon to any measurable degree in my limited experiences with 120hz Monitors and TVs., many people do report suffering from this choice. Perhaps it was early tech teething, I don't know, but it may be a consideration for you.
The shortage of 120hz is a combination of demand (decent) and supply (not so decent) as it is a newer technology, and the companies have a LOT of unsold old tech to get rid of first before saturation.
As for waiting... the common belief is to get what you can afford when you want to have it. If you play the waiting game for cheaper prices/more bang for the buck, you will never be satisfied or done spending, thus negating the whole principle behind waiting.