My hunch is that its not - But let me try to explain our design.  We have a field called "Page Views" which we increment on every page visit for every page in the website.  It's function is simple, increment the page view every time a page is viewed.

Now since we want to grab the "PageView" to do some automation (such as displaying a summary of popular pages) we are calling the UpdateDocumentCache on every page visit - Here's some sample code:

[RestExtensionMethod(returnXml = false)]
        public static int AddPageView(int pageId)
        {
            Document doc = new Document(pageId);
            if (doc != null)
            {
                int count;
                int.TryParse(doc.getProperty("pageViews").Value as string, out count);
                doc.getProperty("pageViews").Value = count++;

                //Get the user
                User user = new User(0); //default admin

                //Publish the document
                doc.Publish(user);

                if (doc.Published)
                {
                    umbraco.library.UpdateDocumentCache(doc.Id);
                }
            }

            return GetPageView(pageId);
        }

I'm probably wrong but this code is neither thread safe or very efficient if called on every page on the website?