Major search engines cache your web pages. You must make your web pages look flawless on search engines' caches or you will miss a big proportion of search engine traffic.
 
Broken Links
     The most common problem with cached pages is broken links. All cached pages are stored on search engines' servers. Any link with a related URL points to somewhere on search engines' servers. To redirect the links to your site, search engines use BASE element (<BASE> tag). But, some links, especially within JavaScript, don't work with BASE element. Those tricky links will be broken when cached, even though they work fine on your site. You can solve this problem simply by using absolute URLs instead of relative URLs.
 
Hotlink Protection
     Hotlink protection is commonly used to prevent copyrighted images from being used by somebody else. This feature also prevents images from being downloaded by cached pages. As long as your pages have good content, searchers will be interested in your site. However, texts which look good against background images may not be visible when hotlink protection prevents the background images being downloaded. When this happens, searchers cannot see anything on the cached pages, so they will go to other sites suggested by the search result.
 

Script
     Scripts, such as PHP and CGI, can be disabled by any websites other than their own. This is a good idea from the point of view of security. But, if you disable scripts from other websites, they will not be executed from cached pages either. Make sure this won't cause serious problems when viewing cached pages.
 
Reloader
     If you use reloading JavaScript, you can automatically send people to your site from cached pages. This sounds like a easy solution for all the glitches. But, keywords used for searching won't be highlighted on your site. Many people view cached pages because keywords are highlighted and it is easy to find what they are looking for. Searchers might dislike you if you force them to visit your site.