I love lilacs. I've managed to squeeze six lilac bushes into my tiny garden and when they're all blooming, the fragrance is wonderful!
The doubles seem to last longer as cut flowers. Someone once told me to remove all the leaves before putting them in a vase because the leaves take the water away from the flowers. Lilacs don't make the best cut flowers but I can't resist bringing a few inside and removing the leaves really works. They'll last 4-5 days without the leaves. I cut a few branches with just leaves to tuck into the arrangement.
Sadly, the lilacs have already faded. I always want them to last longer but maybe if they did, I wouldn't appreciate them as much. It's a long wait until next Spring!