What constitutes being De Facto in a modern relationship?

[Britt]

Well the good news is that the Government around here has finally decided to put in place some laws giving single sex and couples and those in de facto relationships equivalent property rights to those in marriages.
This did however start me thinking.
How do you determine the status of a relationship as de facto? The dictionary defines this as 'from the fact'. I just wondered which fact people current thought this was.
As for me I believe it is having lived together for more than two year. But I would be interested to hear what the rest of you think.

[Ma Parrot]

Two years sounds like the number I recall about commonlaw marriages when I was a kid, but a lot has changed.

Clint Eastwood was shacked up for years, but it still made a drawnout palamony suit.

I think you have to present yourselves as husband and wife.

[Britt]

It is a fairly common figure as is five years, although when you start the timer is still anyone’s guess
The key here is that De Facto is being applied by a statute, to relationships that fall outside of 'husband and wife', so I was wondering what people thought of, as the defining moment in a relationship that moved it from non De Facto, to De Facto.
For that matter what 'stages' do you believe relationships go through and how do you define these stages?
I personally cannot always differentiate when seeing each other turns into dating. I view sex as a fairly definitive landmark in the relationship (usually, but again there are exceptions). Finally moving in together seems to be a fairly identifiable moment (except where you where flatting together before becoming involved). You see the problem so how about some solutions are there any objective standards by which you can judge the stage/state of a relationship?