"With fewer management levels and less money available, traditional incentives are in shorter supply," explains Dr Jane Sturges, a research fellow at London University's Birkbeck College. "In addition, female staff are no longer prioritising them anyway. It's not that they don't value the more established methods of motivation, such as increased money and responsibility. It's just that if their employers want them to give more in terms of workload and hours, then they want rewards that correspond with their lifestyle."
Katie Woolf, a 32-year-old PA from Putney, is a case in point: "I was offered a company car with my job. But I've already got one of my own and couldn't get excited about an upgrade. So I asked for funded training instead, explaining that it would be a long-term benefit to my employer and would cost a lot less than the car. They saw the sense in it.'
Angela Baron, policy adviser for the Institute of Personnel and Development, claims the "psychological contract" between employer and employee is changing rapidly - particularly regarding secretarial work.
"We have recently done some research that involved analysing how companies can gain more commitment and loyalty from their staff - and I was amazed at the number of personnel managers who found that secretaries and PAs are motivated by not just external benefits but, say, the opportunity to take a career break."
But Ben Williams, a chartered psychologist, is far from amazed. "Employers are beginning to realise that money doesn't have a lasting effect as a definition of success," he explains. "Once people get used to their new salary, they start to expect more again, and then become resentful when it doesn't happen. So rather than being a benefit, it can work as a punishment."
Dr Sturges, however, does not deny that money can talk. Rather, she believes that there are four ways in which employees define success. "Climbers", she says, aim for money and status. They don't just want the BMW - they want the convertible. They're usually male and they're the ultimate corporate players.
"Experts", on the other hand, are more likely to be female. They're the ones who want to be good at their job and to be recognised as such. They'll welcome rewards, but value respect and enjoyment over status any day of the week.
"Influencers", on the other hand, are the doers, eager to have a positive effect on the company. You'll recognise this lot by the fact that they stay late. "The biggest motivator they can have is having the opportunity to leave their mark," explains Dr Sturges.
"Self-realisers" are driven by the desire for personal achievement. "They will thrive on being given a real challenge, but they are also conscious of the need to balance the requirements of work with their private life." They'll be the first to ask for time off.
Oracle is one company that is starting to recognise such differences and is responding by offering employees the opportunity to design their own package of benefits. Staff can, for instance, increase their holidays to up to seven weeks a year - a great incentive for those keen to travel but unwilling to try for a sabbatical.
Alternatively, they can bolster their income protection plan to 75 per cent of salary or increase life assurance to four times their salary. They can also choose from a range of benefits, including health screening, dental cover, a company or private-lease car - or they can go for cash instead.
"Effective people-management and marketing is about developing the employment relationship and treating people as individuals with different needs," says Vance Kearney, vice-president of Human Resources. "We already have ideas as to how we would wish to expand this approach to employment to include flexibility of the whole contract."
Bass and Midland Bank have begun developing alternative ways of defining and rewarding success. "Secretaries themselves are usually the incentive," claims Colin Gill, a psychologist. "After all, if you have a PA, it shows you have status. But it's high time companies started focusing on the fact that secretaries themselves need incentives."