Greylisting

We currently use Mailscanner and currently have it setup well we believe and its blocking quite a bit of spam but we are noticing a heavy increase in spam hitting our servers now. However I used to work for a company that used greylisting. It had some issues but they tweaked it quite well. I am wondering if other hosts are using it and if it is working well for them as I've heard of Greylisting deferring PHP email sends from other servers and then blocking and some customers then loosing legitimate emails is this still the case or is it far better than before now as spam seems to be quite on the rise again.