A WebmasterWorld thread has several examples of people who say they have submitted re-inclusion requests months ago and still have not heard back from Google.
A few things here, we know Google Moves Reinclusion Request Form To Webmaster Central months ago. Also, I have tested out the reinclusion request myself with Jennifer Convertibles when they were delisted. And they got back in within a few days. Later, I did a post named Time Line To Get Reincluded in Google With Reinclusion Request where I showed examples of unanswered reinclusion requests and answered ones.
The new WebmasterWorld shows many examples of unanswered requests. I have heard Google won't answer all requests, especially those that still have violations on their sites and those that have repeat infractions - but can all those examples in the recent thread be in violation of the above? I don't know.
Forum discussion at WebmasterWorld.

Comments:
Matt Cutts
03/01/2007 03:10 am
On the flip side, here's a recent comment by someone who did have a good experience getting reincluded: http://www.mattcutts.com/blog/misc-bits/#comment-97880 Certainly lots of sites do get reincluded.
Leon
05/05/2007 05:02 pm
GOOGLE reinclusion! Please follow the link: http://groups.google.com/group/Google_Webmaster_Help-Indexing/browse_thread/thread/56ee5e06e4659c8a/7316fe2d559952d8#7316fe2d559952d8