Style Tiles are an attempt at breaking the Photoshop design comp logjam that exists at most interactive agencies. Customers and marketing folks care tremendously and rightly about branding and the the comp is traditionally the only place that branding is seen during interactive development. But comps are labor intensive, inflexible and, like all other project documentiojn work products unlikely to be maintained through (and certainly after) a project is completed. The style tile places colors, fonts, logos, design elements (drop shadows, boxes/lines, headers, etc. in an easily understandable form, without forcing page designs to match pixel exact approved comps. By separating strategic design from implementation details much less time is wasted on minutia that has little impact on usability.
Paired with Continuous Design (or NoPSD) – a movement towards doing page-level design in CSS as an iterative process in parallel with application development. It’s no magic bullet, of course. But separating the branding and approval side of design, from the implementation side is far more likely to work in a world where design houses are often separate companies or may as well be, even when under the same roof as the web developers who are tasked with implementation. There’s no question that the FASTEST, most exact way to build sites is with a strong designer, who actually understands CSS implementation is able to use Photoshop comps as live development documents – mixing the re-generation of site sprites will CSS to address issues with the correct tool. Unfortunately there aren’t a hell of a lot of THOSE around and not many interactive agencies built around that kind of combined skillset.