I hit 20 last night and I have to say, I am not impressed with the abilities monks get at 20.  In fact, thinking about it, I think level 15 or 16 was the last time my abilities noticeably improved.  It seems like there is a moderate curve in monk abilities from 2-15, and then it really plateau's off.  It's mostly slight to moderate improvements in dps.  Looking ahead, it appears level 22 has some good abilities.  With the new experience table, leveling 16 to 20 took me a bit of time.  I can only imagine how long it will take me to hit 22. 

I have no purpose for this post other than to point out my perception of my monk's abilities.  I'd also be interested to hear from level 22+ monks what we can look forward as we reach those levels.