I guess it depends where you ride.
If you have enough space, it helps to position your bike in an angle to the hill you are climbing and then dismount on the side that is "higher" on the hill (more uphill) - this way you stand "above" your bike when dismounting and aren't in danger of flipping over (I'm not sure if I did a good job describing what I mean).
If you are in a steep singletrail where there is no space to reposition your bike, you can use your brakes to get more grip so you can hold onto the bike while dismounting.

I can't remember any occasion where I was in danger of flipping over backwards, but it can be an issue to have enough standover-height when you have to dismount in difficult terrain.