I been using wings(www.wings.com) for a while now and i like its simetry a lot because of this:
I can easily use any of the sides to tweak;
if i remove one of the sides i end up with a "sillouette profile "where i can have a better view of the model, and not a mesh interior like in lw;
by selecting this blank "sillouette" thing i can flatten it and reqactivate simmetry, it will then bring the other side back on and perfectly aligned...
maybe i should post it in the lw wish list but i want to take my chances in a new thread and maybe one of the awesome scripters here (cman, cim, etc...) can create some plug at least for "tweak on both sides" in simmetry :):):)