Do you think it is a good idea to change a company's logo?

"The logo should represent the ethos of a company and provide a recognisable and clear corporate identity. As the culture and structure of a company changes, it is important that the logo reflects that change. This may result in the modernisation of a logo or a complete redesign as adapted by Amec. Caution should be exercised before an established and recognisable logo is jettisoned. It may take considerable time to get the same recognition." "I think you should examine the commercial effectiveness of your company logo every 12 months or so and then leave it exactly as it is! A logo is a vulnerable thing open to someone or other suggesting a better shape or better colour, or a change to the company name. Why spend loads-a-money exploring an alteration to something you have spent years promoting and which has achieved considerable public recognition? That reminds me - it's about time we considered changing our company logo again. I'll speak to my promotions man!"