Hey PM1111 - I don't think it affects your application. You may be required bit more info of course, but it's nothing really far from someone who's married in paper.
Is your partner under the same 457 visa as you?
I'm on defacto relationship as well for the past 6 years, and on same 457 visa. It wasn't a problem 2 years ago, and it shouldn't be now. We've just accumulated more stuff to prove we're still together and going strong. :-)
My nomination has been in progress, but I'd expect to be approved end of this year only as it has been just 2 weeks now.