Yep apparently there's a chance of doing some serious damage (although I don't know what I never waited long enough to find out)
The light can be kept off all the way to 3000rpm if you drive with a very light right foot, while mine was broken I drove so gently I actually got fuel economy up to 28mpg
I could still get 75mph without seeing the light it just took a veeeery long time to get there, I got overtaken uphill on a motorway by a Nissan Serena once
