Technology, tools, and methods evolve VERY quickly in the Internet. You should review your website every 6 to 12 months. The "latest and greatest" is now over "two Internet years" old (every three months, another software generation is released).
Your competitors who may have been lagging behind when your site was built may end up leading, because they are using better methods. Because of the annual doubling of Internet usage, twice as many people will see the year-old site (now just getting dated looking) than saw it when it was brand-spanking new!
Review these items, asking yourself these questions. Be sure to survey your clients and website visitors (surprise! these might be two distinct groups)
It is important to surf your competitors' web sites, and even to browse other site in unrelated industries (the computer industry is usually the first to use no technologies or techniques). If you are not advancing faster than your competitors, you can quickly lose your reputation as a leader in Internet marketing, and your market share in this new medium.