FWIW, I'm getting a 2009 Felt B2. The whole bike though, not the frameset, as it seems to be a better buy. It was a bit of a leap for me budget wise but I figured I should get the best bike I can afford.
Regarding the Scott v. Felt, they're two fairly different bikes geometry wise. The Felt has a much more refined geometry. Deisgned to be ridden steeper and lower. A little more BB drop, and I like their Headtube angles.
Beyond that assuming we are talking the original Plasma(not the newest Plasma Ltd) vs. the B2, the Felt is better in my opinion in many ways:
1. The Bayonet Fork. Everyone who rides a Felt with the Bayonet fork talks about it's point and go nature. I have not heard one person who does not like the steering of the bike, which is saying something.
2. Aerodynamics. Here is what I want you to do. Go look at the downtube width of the scott, and then compare it to the felt, the Felt is about 25% thinner, that's 25% less to push through the wind. Then look at the seatstays, the cable routing, the forks, the brake placement; Felt did their aerodynamic homework. According to Cervelo's numbers the Scott generates 100 grams more drag at most yaw angles than the Felt. That's quite a bit.
3. You couldn't give me a bike with an integrated seatpost, really. The integrated seatpost on the Scott is a deal breaker to me. Before you buy it, try putting it in a bike case.
4. Cable Routing - Felt has the best internal cable routing in the business. It's funny to tout something so small, until of course you try and change your cables.
To me, the three best, and most proven, triathlon bike designers out there right now are Cervelo, Felt and Trek. They have competitive prices, smart specs and all of them design in the wind tunnel.
Bikes I would consider if my favorite shop carried them are Cannondale and Specialized. Both bikes have kind of screwy geometry(which a 54cm C'Dale Slice would for me) but if they fit you, they are both quite nice.
There are other companies I would most definitely consider, such as Jamis, Argon 18, and Blue; these companies seem to be doing some smart things with their bikes as well.