Against the 'necron air force' (armies that consist of almost purely destroyers), I tend to do decently. If they're taking almost purely destroyers, they won't have the points to bring a monolith, and therefore if you can get into HtH with them, that entire squad's effectiveness is pretty much shot for the rest of the game. How to get them in HtH?
Being a Blood Angels player, I generally turbo- boost my MM bikes toward the destroyers, making them pretty difficult to kill if the destroyers decide to fire on them. If the destroyers decide to stick around, I can tie them up in CC almost indefintely. If they decide to run away, they'll have to turbo away, and therefore can't shoot that turn anyways.
Also, making use of a Callidus assassin will stop one of the squads, and eventually destroy it.
Against destroyers sitting in the back shooting, just take a turn concentrating on shooting them, they'll die easily enough, and if you kill all of them in a turn, they won't get WBB.
In my opinion, normal destroyers don't do a lot of damage to a marine army. Sure, they can hurt your vehicles, but with BA thats not going to matter a whole lot anyways, since all my vehicles don't do much vs. 'crons anyways.
Heavy destroyers can do a bit more damage, but if you use the same 'concentrate fire on all of them' tactic I talked about earlier, they won't end up hurting you too bad either. I guess in the end its all about target priority and massed firepower.
Thats no moon, thats a... no wait... thats a moon.
Jesus saves... everyone else takes a wound.