Forager/draw-to-X seems like a strong tempo-building combo. The premise is simple: use Forager to clean out your hand, and draw back up. Forager serves the same purpose as any virtual coin, but it cleans out two hand slots instead of one. Plus, it gives a buy and thins your deck.
The weakness of Forager is the same as any of the discard-for-coin cards (Horse Traders, Secret Chamber [but not Vault because Vault draws too])—you're paying for the cash with both the discarded/trashed card slots in your hand and the card itself. By default, Horse Traders has a per-card value of $1 (use 3 cards to get $3); Secret Chamber is a max of $0.8 without draw; Forager is $0.5 if there's a Copper already in the trash, which makes it worse than Copper. But, because the draw-to-X cards love handsize reduction, Forager's drawback of shrinking your hand ends up as a benefit.
It's especially potent with Jack because Jack can't trash your starting Coppers, while Forager prefers to eat at least one Copper before starting in on the Estates. And, since Jack is flooding your deck with Silver, it's not a huge loss to chop a Silver in the mid-game to power up all your Foragers. Use Forager, and Jack becomes +3 cards (with filtering), +1 coin, gain a Silver.
The drawback is that your opponent can benefit from you powering up the Forager, especially if you trash a Silver or more valuable coin. But, the tempo lead from the increased cycling (copper trashing as well as the extra draw-to-X benefit) probably makes it worthwhile in most circumstances.
