We are planning on restructuring the URLs in our content management
system to be more search friendly with keywords rather than id
numbers.  The URLs will exist in the old and new formats for a short
time but soon the old versions will not be live on any of our sites
and we will only display the newer versions (though they will still
exist).
We want to use a 301 redirect from the old versions to the new
versions.  However, in order to avoid performance issues we are
planning on only serving 301 redirects to the search agents and not
human users.  I am wondering if Google will see this a cloaking in any
way since a spider is redirected but not a human user?  Wouldn't the
Google index only show the new URL once the redirect has taken place,
therefore showing the human user clicking from a SERP the same link
&page as the spider is given?  It is a big change and I want to make
sure we are staying within the Google webmaster guidelines while
maintaining our search strength.

- vshen -

If you haven't started on this: avoid it and do the 301 redirect for
all users, spiders or not. The problem is that users who are served
the new content on the old URLs are likely to link to the old URLs.
This can cause a problem in that Google will not spot many new URLs in
the new links to your site. Additionally, it sounds like a pain to
maintain :-)

That said, you're likely not to have direct problems with Google with
regards to this. In your situation however, I would prefer to make
sure that it's all clean instead of "likely not having a problem" :-).

John