SharePoint is not a meta-directory, so it cannot synchronize back to AD. This
is a design decision by the product team. You might want to look at
DeliverPoint (www.barracudatools.com) if you need to manage users who have
transferred, moved on or need to be cloned across your SharePoint farm.
DeliverPoint will allow you to transfer, delete or clone permission sets for
users or groups at the farm, virtual server, managed path, site collection,
portal, site, area or sub-web levels.

If you are having issue of AD updates  not being imported read this
article.

http://support.microsoft.com/kb/889385

I found that it looked liked the updates had been put in, (showed
the correct email address and everything) user  could get an alert.
His email address had changed in AD. When I deleted and added him to
the site, the old email address came up. Sharepoint stores this
information once a user goes to a site. There is a hot fix for the
issue.

Was this hotfix rolled up into SP2?

I wasn't very clear in asking the question. Here is the question:

I know sharepoint  to AD is not possible out of the box.
Q. AD import to Sharepoint is good as long as a new user  is added to AD. Then we can see this user in Sharepoint. But, lets say, in AD an existing  user's record is updated with a manager's info, this manager's info is not reflected in Sharepoint during AD import.

it should be under both an incremental and a full import. Does it not appear under either import?