There is an excellent thread at WebmasterWorld on the topic of search engine position security. In short, the SEO is asking others, how secure do you feel that your rankings won't change all that much? How secure do you feel in your site's success in Google? How secure do you feel that Google won't change things up so drastically that your site won't be impacted?
Why should you feel nervous? Some of the points in the thread include the fact that Google is showing "universal search" results, such as videos, local, news, images and so on in the main web results. Also, Google is constantly changing up their filters and now working on releasing a new infrastructure. Plus, you need to constantly maintain your site, in some industries, to remain at the top.
How confident are you? Take the poll:
Overall, there is some excellent SEO advice in the thread, outside of the question in this post. But please have your SEO buddies that this anonymous poll.
Forum discussion at WebmasterWorld.