It happened... the interior driver door, when unlocked (by key outside or by remote) will not open. Pulling the interior door handle gives no resistance like it did when it worked, and the door opened.

As a bonus, the remote locking mechanism will not work on that door either. It appears the two are related.

Yet, the door will lock by key (from the outside, of course).

Update from Aug 31, 2009: The repair was covered under warranty, which meant it had to be serviced by someone other than my mechanic.

The repair place showed me the front-left interior door handle (module) (Part #6E5Z-5422601-A) they had to replace. A pretty solid plastic-made component; except for one thing... the end of the door handle itself (located inside the door when installed) broke off, revealing it to be a very cheap piece of plastic (the piece had a silver-like coating, but in its center was undoubtedly plastic)... looks like solid chrome, but... That door handle rendered the whole $36 module inoperable. Hmmm...

So, the whole front-left interior door handle (module) was replaced, and in 1hr, the repair was complete.

Update from Mar 14, 2011: it appears the oem version of the door handle was designed (on purpose) to have a chrome appearance, but a cheap plastic part.

Found a new oem module online (matching part#), and had it installed. Unknown how long this will last...

Had to replace it with another module at 80000 miles