Design on the web is a different animal than design for print. Grid systems provide a basic framework for page layout that provides a structure, consistency and coherence to a design. However, HTML and CSS provide some challenges when dealing with complex layout structures. Best practices in web development means that the methods once used for layout by using tables to establish grid structures have fallen out of favour and have been replaced by POSH -- Plain Old Semantic HTML. Many site layouts created during the early development of Web Standards and the early adoption of CSS and semantic markup favoured a simple one-, two- or sometimes 3-column site structure. It may be a good idea to keep layouts much simpler.
However, designers like to have the flexibility of a strong grid system to help give layouts a much more refined and sophisticated aesthetic.
Several CSS frameworks are available to help build layouts quickly and easily, without worrying about whether the layouts will work across various browsers.