Anyone got experience of getting/trying to get one of these?

My girlfriend, who's a teacher, is looking into doing this. As far as I can tell, the deal basically seems to be that a government-sponsored housing agency loans you between 20% and 40% of the value of the property - pretty handy in the current climate when you have little or no deposit to offer - then when you come to sell later on, you pay back the same percentage, whether the value went up or down.

Which alls sounds good on paper, but wondered if anyone here knows of things to be aware of, drawbacks etc?

(Plenty of DiSers are police and nurses, right?)