Is it OK to have Search Engines Skip Ajax Content Execution?

[friendoffood]

I recently added some ajax pages to automatically fill in small areas of my site upon page loading.  That is, the user doesn't have to click anything.  Therefore when Google and Bing crawl the site the ajax is executed too.  However, my understanding is that does not mean Google and Bing are also crawling the ajax content.

I actually would prefer that the content  would be not be executed OR crawled by them.  In the case of Bing I would prefer that the content not even be executed because indications are that the program exits the ajax page for Bing because Bing isn't retaining session variables which that page uses, which makes me concerned that perhaps when that happens Bing isn't able to even crawl the main content..dunno..So, ajax execution seems potentially risky for normal crawling in this case.

I would like to simply have my program skip the ajax execution for Google and Bing by recognizing them in the useragent and using an If robot == Y skip ajax approach.  I assume I could put the ajax program in the robots.txt file but that wouldn't keep Bing from executing it (and having that exit problem mentioned above).  It would be simpler to just have them skip the ajax execution altogether.

Is that ok or is there a chance the search engines will penalize my site if they find out (somehow) that I have different logic for them than for the actual users?  In the past this surely was not a concern but I understand that Google is increasingly trying to become like a browser so may increasingly have a problem with this approach.

Thoughts?