Dynamic links, redirects, cloaking and dup content

[moltar]

Lets say I am making some sort of counter. Users are able to place a counter on their website. The counter image (or text) will link to my site like this:

.com/counter.pl?service=abc&login=def

If a real person clicks on the counter, it will go to my site, and then redirect to another user's site (depending on the service name). It counts that site's traffic.

If a search engine follows the counter link, I want to either forward to my counter's site main page or just display main page (without redirect).

I was wondering:

• Will be of any value to redirect to my site in terms of SEs?
  
• Will it pass any PR?
  
• Will it be considered bad cloaking?
  
• If I display the same page (i.e. index page) for different URI strings, will it be considered duplicate content?