We have an interesting 'bug' in our JS code that only fires when a user agent has a specific combination of parameters -- specifically when IE8 sends both Trident/4.0 and MSIE 6.0;
We have checked the GA export data; it appears to export only the pre-digested browser information: http://code.google.com/apis/analytics/docs/gdata/gdataReferenceDimensionsMetrics.html#browser.
Forum post 87919 on forums.digitalpoint.com (link removed since I'm a n00b) refers to pulling a cross-segment report for more detail; however, that no longer appears to be on the GA front end interface.
Why do we need this instead of just fixing it? If it turns out it only impacts a few users, we can schedule the fix later in the cycle; if it's impacting 20% of our base, it becomes far sooner to fix.
So, the question - how can we pull a specific User Agent string from GA; pull all UA strings from GA or run a Regex against GA to get a count of a matching UA string?
We're also working with the SA team to enable UA logging on the apache level (very high volume website; logging is turned way down).
The best you're going to get out of the Data Export API (or the Google Analytics interface) is processed information: browser / browser version (Internet Explorer / 8.0). There is no way to get the original user-agent string.
Also note that if you have a high volume website you're going to run into data sampling especially if you're looking at a date range beyond larger than a day or two (more on sampling).