taking time to deforest will screw over your own team through your absence from the battle area.
Acro's quite used to screwing over his own team.
I never ever deforest, and when someone deforests me, I usually ask them to stop. I consider it very poor etiquette.
Don't get me wrong, it's a very effective tactic; I just don't like to win or lose games that way. I feel the same way about pooping mines everywhere - it just makes the game less fun.
On the other hand, some people are completely against walling in builders, and I think that's a totally legitimate thing to do, so I guess it's a matter of personal preference.
If I had to rank these three tactics from worst to best ("worst" meaning most game-ruining, not least effective) , I'd say:
1) Carpet-mining. I quit once this starts.
2) Deforesting. I ask people to stop, but continue to play.
3) LGM-walling. This is a fine tactic, I do it to others, and don't complain when they do it to me (which they do quite frequently).
Just my $0.02
CF