Quote from Google's blog:
As the web continues to change and evolve, our algorithms change right along with it. Recently, as a result of one of those algorithmic changes, we've modified our webmaster guidelines. Previously, these stated:
Don't use "&id=" as a parameter in your URLs, as we don't include these pages in our index.
However, we've recently removed that technical guideline, and now index URLs that contain that parameter. So if your site uses a dynamic structure that generates it, don't worry about rewriting it -- we'll accept it just fine as is. Keep in mind, however, that dynamic URLs with a large number of parameters may be problematic for search engine crawlers in general, so rewriting dynamic URLs into user-friendly versions is always a good practice when that option is available to you. If you can, keeping the number of URL parameters to one or two may make it more likely that search engines will crawl your dynamic urls.
Link to the new webmaster's guidelines: