Yeah, I already picked up Haulin USA.
As for how it is, Honestly, I've never played the game. This despite the fact that I picked it up during the 2010 Holiday sale. But at that price, and considering how expensive the DLC is, I had to pick up that pack.
I store all games that I buy in my inventory, so if I play Railworks and like it, I can add the pack later. If not, I figure I've got an excellent shot of at least breaking even on the deal if I try to sell the pack off.
If you have even the slightest interest, now's the time to buy.