Industry practice for cross country pipelines is DH progression. The thickness of pipelines does not lend itself to UH.
DH progression in Xcountry has proved itself to be more than adequate for the service.
Also a open root UH progression bead, even with E60, 70 and 80XX would be very slow and if the project has double joints, 80 feet of pipe hung out for the bead would be very difficult, And if the project would have open root with LH, it would take even longer.
I have seen UH progression used in repair work on raw natural gas lines to unknown grades and carbon content of pipe in sour service when underbead cracking is anticipated due to the hydrogen content of the gas. If the gas company is anticipating a lot of repair work on a pipeline section and the pipe is a unknown grade and carbon content, it is common to remove a joint to run metallurgical and welding procedure test to prevent having to use UH progression.

Marty,
We recently began a rather large scope of work wherein the customer was originally specing B31.3 and then switched to API 1104. Ours is all shop work (skids and such) but we still qualified a butt load of API 1104 quals to comply. We do not have an excess of guys polished on DH cellulosics so we ran our standard processes under 1104 (GTAW roots with 7018/8018 SMAW and FCAW and SAW utilizing N1's for the higher tensiles).
We have been competative against contractors used to utilizing DH SMAW and made money. Of course our UH is predominantly FCAW which is very competative with DH cellulosics (you do not have to stop to change electrodes), and we do have some heavier walls to deal with though not exclusively.

Skill level is always a factor of course, but the potential for productivity with FCAW exceeds anything SMAW can even come close to.
Deposition rate, the ability to run bottom to top without stopping, less grinding, less slagging, less stub loss, the ability to carry more metal (especially at the 9:00/3:00 positions).
The interesting thing is, going to bigger wires does not give you greater deposition rates. It actually gives you less due to I2R heating and arc density. However, the bigger wires do have a capacity to accomodate more current which can manifest as greater deposition in the right hands.
SMAW isn't the favorite of piplines because of its dominant productivity. Its the favorite of pipeline because of its convenience, field versatility, and acceptable productivity.
In the field I would choose SMAW (cellulosics for pipeline/LH for industrial) almost every time myself. That is where it shines. But when it gets right down to it API 1104 is essentially process neutral and if alternative processes offer an advantage I would make use of them.

PS: I've run into a lot of welders that would rather change electrodes. But I always argued I was saving them money on cigarrettes when I insisted upon FCAW........Just kiddin. 

I believe the preference for DH on pipelines was in existence long before there were higher yield materials (utilizing V/Nb/etc.) wherein the greater control of the HAZ could make or break your qual and your weldment as far as yield/tensile was concerned.
Also, there is nothing that says if you do have this issue you cannot control it with UH. We did it. And very successfully with V/Nb type alloyed X70 materials.
Also, even though it doesn't necessarily qualify as UH or DH (being a 1G positionas such) double joint racks have been using SAW for decades that traditionally is considered a higher heat input process.

Thanks all for the replies.  This has been very educational for me.  We recently had 20 miles of 30" natural gas pipeline installed and are now looking at 60 miles of 16" CO2 pipeline.  I guess I already knew there was a preference for DH root passes on pipelines, but did not realize the whole weld was DH.