Top 10 Reasons for performance issues with you website

There is big number of blog posts regarding web site performance, but here is my top-10 reasons from number of real world websites affecting their performance:

1. Table based layout – especially sensitive performance degradation with IE, big number of nested tables also make it look really tricky during the loading time in Firefox and Webkit
2. Superfluous  markup elements – when they are part of repeated elements such as grid or list this results in hundred kilobytes of useless content
3. JavaScript included in the wrong place – this pushes web browser to load/execute JS before you will see the first byte of visible content
4. Lots of HTTP errors, especially 404 and 503 – broken links, moved images, incorrect relative paths to resources
5. Duplicate <link> blocks and JS includes – obvious, but still common problem
6. No caching (content expiration) is set for static resources – both server side caching and content expiration headers for the client
7. Inline <script> blocks
8. GZIP compression is not enabled for CSS and JavaScript files
9. Number of JavaScrip includes for one page – results in big number of network connections, sometimes preventing page to render correctly
10. Incorrect or broken HTML markup – browser spend more time than expected to understand what you were trying to say with <table><div><tr></div><td></tr>/>