Well, I'm hardly the expert (there are plenty more experienced players than me who'd probably have better answers) ... but my take is this: let's make the assumption that, by definition, a calling station will always call if he has any kind of made hand (even low pair). If you are in any kind of situation where you have some kind of draw (probably the worst situation you could be in at this point), you are going to get called all the way to the river. Basically, you must make your draw, and you have to hope that in doing so, he didn't redraw a better hand. OK, so that situation's pretty straightforward: whether or not you had the better hand pre-flop, you are now basically on a gamble. Low EV = bad play. The only situation where this might be different is if you've got a monster draw (say, 15+ outs on the flop) - then, you are probably getting good odds to keep going, and in the long run you will have +EV. But this is not the most likely scenario when you have a draw - so my guess would be that you are still probably negative EV (though possibly not by much).
Let's take another situation: suppose you have a made hand, but it's not very strong - say mid-pair, decent kicker. Let's assume that the calling station you're up against also has a made hand - obviously, if he's got a better hand you're in trouble. But what if he has a lower hand than you? OK, so now he's basically drawing to beat you. The bigger you make your bets, the better the odds you give him (remember that per our assumption he will *always* call, no matter what!). So you can't really bet big. Now let's look at betting small - again, he's going to call! So maybe this is the best possible situation for you, because at least you're building the pot with a made hand, and you're hoping he won't improve by the river. All in all, not a great situation - probably a marginally negative EV, since on the times you'll win, you won't be likely to win much (you have a modest hand, and so it doesn't make a lot of sense to keep overbetting the pot in the impossible hopes of scaring off your calling station.)
Finally, let's take the situation where you've flopped a monster hand (e.g., flush, straight, boat, maybe even top set or trips on a rainbow/unconnected board). This is probably the only situation where you are all but guaranteed to win. Certainly, if your hand holds up come fifth street, you are going to be very happy and have huge EV. But what percentage of total scenarios does this situation fall into? Not a lot!
What's the conclusion here? A calling station can stand to make you a lot of money - but only when you are absolutely positive you've got him beat. So unless you're in it for the gamble, all other times, you have a mediocre shot of winning, and when you do, you will probably not end up with a huge pot.
Now you're probably looking that over (as I just did) and are realizing that I assumed that you are heads-up with a calling station. Well, at a 10-handed table, this is perhaps less likely. But at a shorthanded (e.g., 6max) table - this is exactly what is most likely to happen! (Unless, of course, there are some particularly loose types at your table.)
For the sake of satisfaction, though, let's look at what happens even when you have a modest to large multiway pot - well, you've now stacked the odds even further against you. You have zero chance of getting everyone else to fold with a marginal hand and a big post-flop bet (because of the calling station, who you know will call you all the way down) - so the best you can hope to do is get heads-up with the guy. But then you're back to square one!
So - all in all? Having to play with a calling station at your table is not the most favorable situation to be in. Basically my take is, that if you're looking to maximize EV, facing a calling station is a poor situation to be in.
Any rebuttals? Did I miss something in my (novice) analysis? I'm looking to learn, too..