Should I stay or should I go?

Keeping hold of staff is going to be the biggest challenge HR professionals face this year, according to a survey by US firm Taleo. This isn't a surprise in what is now an employee's market. Employers will find themselves increasingly required to get in line with what employees want, and if they don't they risk losing the battle to attract and keep the talent needed to stay afloat.
The golden age of a job for life that we all hark back to may be something of a myth - even in 1985 only 10% of workers had been with the same employer for 20 years of more. But we have so much choice now that our careers are characterised by a series of job-hops.
I used to be a great believer in job-hopping, but my opinion is changing. I wonder whether I am alone now in finding the idea of sticking with one company very attractive. Not least because during my working life I have witnessed a number of promotions being awarded partly as a result of longevity of service.
My friends who have shown commitment to their companies seem to have achieved a greater depth of satisfaction from their working relationships and a much better work-life balance - all from staying put and growing their role from within. But is this possible if you are at a company where there is no clear career path?
What is best for your career - to stay or go? Have you benefited more from changing jobs every two years or have you been more rewarded by growing with one company? Where would you be now if you had stuck with your first job?