The couchsurfer may arrive with assurances that 'it'll just be for a few days', but many Sydneysiders find days turn into weeks or months.

For the more affluent host of an unwanted couchsurfer, their presence is little more than a temporary irritant - a freeloader who is likely to drink all your beer and monopolise the remote control.

'Professional nine-to-fivers, modern couchsurfers are either saving for a million-dollar bond [or] have been forced out of their abode at short notice,' wrote journalist Lauren William recently. 'But gentle host, be warned. You may have landed yourself a cleverly disguised long-term flatmate.'

William compiled a list of rules that the owner of the couch should impose on any occupant: never allow the couchsurfer to unpack; never allow them to hang pictures; and never allow them to weed the garden or feed the cat.

'The modern couchsurfer will cook and clean,' she warned. 'Their desperate longing for a sense of tenure would otherwise make them the perfect house guest.'

Despite its humorous image, couchsurfing has a more disturbing underbelly. Faye Williams, executive officer at a government-funded tenancy centre, says that many of Sydney's couchsurfers are often in dire circumstances, with limited long-term housing options.

'When people are desperate, they'll turn to friends, relatives, even someone they've just met in the pub,' she says. 'To me this is ... just another form of homelessness.'

Tenant support groups report that today's couchsurfer is not necessarily young, single or university educated. Faced with high rents (they increased by 12 per cent last year), a growing number of poorer families are forced into temporary accommodation, such as caravan parks, boarding houses or a friend's spare room.

Authorities say there is a new class of homeless people emerging, especially in the western suburbs, where families are struggling to pay bills; almost 2,000 families were evicted last year.

'In the current rental market, families with young children who have been evicted are finding it difficult to find accommodation,' says economist Harley Dale.

'Those lower-income households are getting squeezed out of the market, and there is a risk that if we don't fix the problem, we will have - in three to five years - a whole new class of people that can't be accommodated.'

The irony is that many couchsurfer hosts are themselves living in substandard or overcrowded state-owned housing. And those who may feel superior to their well mannered yet unwanted house guest should heed the example of William, who joined the ranks of the couchsurfers.

Like most of her couch-squatting compatriots, she is finding that her temporary homelessness is becoming permanent. 'Despite leaving my lentil-eating, nose-pierced, Chomsky-quoting student days behind me, for the first time I can truly claim to be of 'no fixed address'.'