I'm intrigued as to what prompted the original post, as it sounds a bit on the defensive side. And I'd disagree that it's less nerve-wracking when you're more experienced. It's scary in a different way when you're more experienced, especially if you're the booked guest, because much more is expected from you and you'll have high standards for your own delivery too.
People have made some good points already, but I'd say the paramount thing, whether in a singaround or in a formal performance setting, is that you're choosing to sing to other people and therefore you need to pay due respect to that. It's not the same as singing to your bathroom mirror, or humming along to a recording, or even singing in your car and you can only learn performance technique by singing to an audience - but I hate the "good enough for folk" phrase, whether for tuning or performing, and I suspect a lot of other people do too.
So I suppose what I'm fumbling my way to saying is that there's the question of learning the song or the tune and its accompaniment (if it has one) on the one side and then there's performance technique on the other. As long as you've learnt the song and all that goes with it for a singaround (or you know the audience is tolerant enough to cope with bits of paper or songbooks) then you probably don't need to worry overmuch about performance technique until and unless you're the star turn. But if you're taking yourself and your music seriously then you need to keep cranking it all up a notch or two. You won't stop being nervous - I think that when I stop being nervous it'll probably be time for me to bow out gracefully, because it will mean I've stopped worrying about my audience.

Anne