Opions, people, just my opions:

1.) Why are road bikes better at climbing? - Generally lighter and you can actually change gears as you ascend. Novel concept.
2.) Are tri bikes uncomfortable out of aero? I think they are ucomfortable all of the time. But that wasn't your question. If you look at most integrated bars, they have very limited hand placement (mostly because the design assumes you are in the aero position with your hands on the bar ends and you get just a tad bit of real esate to put your hands when you brake). What would be the lateral portion of a road bar is flattened into an air foil which really isn't intended to be held onto. You may have simple bull horns which may have more room for hand placement. But even then the bolted-on arms rests take up a lot of space on the bull horns. Also, you lose all of the benefits of the aero tri bike when you aren't in an aero position. So when you aren't riding in aero, you are stuck (on integrated bars) with mostly one hand position.
3.) If you have proper clip-ons are the shifters on the breaks or at the top of the clip-on?? One benefit of clip-ons is they are designed to work with a road set up with no reworking of any cables, requiring nothing more than a mini tool to attach/detach. With clip-ons, the shifers stay on the road bars, integrated with the brakes. I guess you could re-tro fit them and take the shifter cable out of the Ergo/STI* and thread it to the bar end and keep the brake cable attached to the Ergo/STI, I'm not sure though. That seems like a lot of work.
4.) Carbon vs. Aluminum? - I'm going to leave that one to Sheldon Brown's article on frame material (disregard that he directed it at "touring.")
5.) Any other ideas?? - Try 'em all before you buy.

*Campy Ergo Levers and Shimano STI

1) A few reasons that Sooner mentioned along with...your position on the road bike is more suited for cranking up a climb and activates some different muscles. Also, this may not be the case for everyone, but since I am more compact on my tri-bike in general (b/w saddle and cockpit) I have some interference where my knees can contact the cockpit (armrests, particularly) if I climb out of saddle on the tri-bike without thinking about it.

2) I don't think tri bikes are uncomfortable riding the bullhorns, and I have to relatively often to get out to some open space to get down and aero. The shifting not being there is annoying in that case though.

3) not shifters on clipons as stated above

4) not going to touch that...I have an alum roadie (although it's an entry level bike, so I didn't really have options at the time) and a carbon tri bike...love them both in thier own ways

If it's going to be your only road bike (non-mountain)...I'd go with the S1...I certainly wouldn't want to do all my training on my tri bike, especially since it's far less agile and reactive to the road bike and nearly impossible to ride with a group...at least if your group attacks on hills, has some friendly competition, etc...(if they even let you try)

What he means is that when you're climbing a steep hill (or a rolling hill if you're not prepared correctly for it/trained to climb in aero), you're going to be riding on your base bar (bullhorns)...which means your hands will have convenient access to the brakes, but the shifters will be at the end of the aero bars. You can definately still switch gears while climbing on a tri bike, but it requires moving your hand out the the shifter and flipping, which can disrupt balance and tempo especially if you're really cranking (exceedingly more difficult if you're climbing out of the saddle, unless you have very solid handling skills or are very quick)...whereas, on a road bike it's a the shifters are at your fingertips while climbing, so shifting is much easier on the fly.

Also, this article may help, Gordo is definitely an expert on anything triathlon/endurance sport related. http://www.xtri.com/features_display.aspx?riIDReport=5838&CAT=23&xref=xx

Interesting thread and something to think about. I have been trying to decide whether to add clip ons with the flip up rests to my roadie, stay with the traditional road set up, or just swap out the whole road bar setup for a bull horn with clip ons, end shifters and ad a forward seat post....(new bike not an option right now)

Good info...

okay - got it thanks....

I agree with you...I wasn't arguing a road bike is better suited for everything...if that's the case I wasted a lot of money on my P2 this year. I was just answering maggie's question about shifting while climbing, in which case what I said is true.

Overall though, you definately get more versatility from a road bike w/ clip-ons than from a tri-bike, so if you can only have 1 or the other...I'd go road. However, if you can manage to have both...all the better. I'm very comfortable on my tri-bike, and love to sit in the aero tuck and hammer, particularly on flats. That being said, my 5 year old aluminum LeMond w/ Ultegra/105 blend (inferior in every way to my P2) still calls to me since it offers a little more freedom and a different experience I can't get on my tri-bike.

I'll second this. I went from a P2SL frame to a P2C this year. Identical geometry, identical components (I just moved them from one frame to the other), and I'm riding just a bit lower in front this year. There is no real noticeable difference in ride comfort, except maybe I don't feel quite as beat up after 100+ mile rides. The P2C has some slight aero improvements over its aluminum cousin, but I think if I were only doing HIM and shorter racing, an aluminum tri bike would work just fine.