The Problem Report:
In the Apple Address Book application, the File > Import > Text File… does not work for me. I get the field-mapping dialog and I can match up the fields OK, but then:
+ The OK button doesn’t do anything (that I can tell).
+ Clicking the right arrow to see the first imported record works, but the left arrow is still grayed out. If I keep clicking the right arrow until I reach the last record, the right arrow grays out and the left arrow is enabled and I can back up. When backing up, both arrows are correctly enabled.
+ When browsing through the records, the spinning gear next to the arrows appears and never disappears, even though the next card has been displayed and I can go to the next card.
+ Cancel does work, and seems to be the only thing I can do.
unsolved (and thread closed) at:
http://discussions.apple.com/thread.jspa?threadID=2289716
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The Explanation:
Garbage characters can become part of your text file, especially if that text file is an export from another address book application, and especially if some of the data originated from a previous address book program. In this case, some of the data was well over 10 years old, and had come from a Sharp Wizard, exported to a Mac SE/30, several Macs, a Palm 3, then a few more Palm phones, & NOW Contact (NUTD NC).
Tragically, Apple Address book does not report this corrupt data as the problem, it just gives zero feedback and doesn’t work, leaving the user wondering why.
The Fix:
Open that text file in a plain text word processor, the free TextWrangler is great. (MS Word is NOT better for this.)
Search for odd characters, which may well be in a different color, and some may look like upside-down question marks¿. Those are the likely problems. Other problems may look like the backwards P, ¶ paragraph mark (aka Pilcrow). In this file we are only expecting to see the sideways L as a line ending, 
not the pilcrow ¶ . However in some cases, the pilcrow is an acceptable character.
A quick way to replace the bad characters is to pull the “Text” menu to “Zap Gremlins” and let it replace any control characters with a bullet • (option 8). This will not nuke your vertical tabs, which are non-ascii characters. Vertical tabs are what was used when you thought you’d used a return in a database field. Here’s what the “Zap Gremlins” dialog box looks like in TextWrangler.
Then “Save As…”
Ok! NOW your text file WILL import into Apple Address book. Yay. You just needed a “clean” file. :-) Actually, this technique will probably work out well for many different applications.
If you plan to continue using your NOW Contact file (or other source file) and you can spend a little more time now to save some time later, then go ahead & use TextWrangler to “Find” each bullet • (X the box to start at top) and then look up that same record in NOW Contact and fix it at the source. Those bad characters will usually show up in NOW as a hollow square character. If you fix it at the source, then this problem might really go away forever!
This was done with Mac OS X 10.5.8 Leopard, but may apply to most/all versions of Apple Address Book to date.
Dave Nathanson
Mac Medix