Honestly, I believe that the current talk of a possbile UAL-U codesharing deal is little more than wishful thinking by emps. and shareholders at both airlines.
On the UAL side, at least ALPA is beginning to realize that the current gravy train is unsustainable. The company BADLY needs additional revenue to justify the avoidance of STEEP (30-40%) pay concessions and layoffs that will occur either with a loan guarantee or a formal BK reorganization.
On the U side, it should be remembered that Chairman Steve Wolf was not retained to establish a codeshare or partnership deal with another airline. Wolf's mission is to sell US Airways by any means necessary. Siegel the Newbie could have brokered an alliance all by himself; the BOD wants Wolf's expertise in brokering good airline deals in order to finally end the madness, so to speak. Therefore, IMHO, any "alliance" talks with UAL or anyone else who is not serious about a merger are just diversions while the "big deal" is being negotiated.