Ouch. lol.
I spent $350 on a brand new 20" ADC monitor about a year ago. Even now, I'd have considered it a no-brainer (I bought a 23" brand new ADC a few months ago for ... $675... before the 2209WA came out!) LOL needless to say I have my dream setup.
So take what I have to say with a huge grain of salt eh?
The 20" ACD has a higher pixel density and a great S-IPS screen. The aesthetics of Apples' displays are second to none, and if you have it on a table in the middle of the room or something.. fricken awesome.
However, you're comparing a brand new screen with a GOOD 3 year warranty to a used screen with no warranty, questionable usage history, and a questionable future.
If the ACD was a little cheaper, I'd think about it - but all of my computers sit on tables, and not on those "computer desks" with hutches, so I do enjoy my aesthetics and I will sacrifice in other places (like my cable bill), lol.
Yeah though, the 2209WA is a damn good monitor, I know it's ironic to say that for a screen I've never seen in person, but come on, it's an E-IPS screen for $300 and the in the pics I've seen, it is.. quite nice compared to a TN/MVA screen, just like an S-IPS screen would be.
Go for that 2209WA unless aesthetics matter *THAT MUCH* to you.