Taglines are the first step and an integral part of brand building. Their value builds for years, and over time, a good tagline can be your best and least expensive form of advertising. If your company name, logo and tagline are all working together as they should, they become an ad in and of themselves.
No matter what your company does, your tagline creates a first impression. People will remember a tag phrase even before a company name. Having years of equity built up in an old tagline can work for or against you. Is the phrase you're using "dated?" Are people tired of hearing it - or worse, no longer believing the claim?
A tagline older than 25 years is usually a sign that your company identity needs reinvigorating. It's never too late to change a dull, tired, non-communicating tagline. Even the biggest brands with famous taglines change their slogan every few years. Most people remember when Coke was "The Real Thing," but look at all the other taglines they've used over a period of 20 years:
For some strange reason, few websites have taglines. This is a shame because those companies (and individuals) are missing out on a prime opportunity.
Any company with a website should make sure to have their logo and tagline on every page; it counts as "an impression" each time a viewer sees it, and when a potential customer prints out a single page from your site, you want your company identity on it.
Few designers or webmasters realize that taglines create a first impression and communicate just as much -- if not more -- than a fancy home page.