Seems pretty much hit-and-miss. Re: Boraxo's experience with Air Canada not posting UA miles, I've had the opposite experience. Never had a problem with getting AC miles posted to my UA MP account, whether it was an AC flight# or a UA codeshare. I don't doubt that Boraxo and others had problems though; sometimes it even seems to depend on which station was involved.

I did get really bothered that because I was going BOS-YYZ-YVR, YVR-YOW-BOS I only got 50% miles for the Toronto-Vancouver and Vancouver-Ottawa legs. Should have read the fine print on UA's site about AC. But that's not their fault, that was mine for not checking the conditions for discount fare earnings. AC did post to MP exactly what they should have - just not what I'd hoped for.

I've since learned my lesson, hence my opening up a LAN account for oneworld airline earnings so that I can get credit for my intra-Argentina discount flights on LAN Argentina that wouldn't count for AAdvantage. The downside to these partnerships is that they have a lot of uneven conditions. The upside is that you often can find a way to work around it by joining another program in the alliance. I figure that this year I'll post all my AA flights to LAN instead of to AA, along with those LAN flights. Throw in a few HHonors double-dips (at 1000 LAN kilometers per stay) and I can score a 40k (slightly less than 25,000 miles) domestic North America reward on AA or AS. Since I wouldn't have a shot at getting status on AA anyway given my usual travel patterns, this works out well. Plus it gives me a program that lets me earn credit for BA US-UK flights that aren't valid for AAdvantage, in case I ever take the convenient DEN-LHR nonstop.

Of course all that assumes that the partner credits post as planned. The whole topic of this thread.

Oh one other thing I do, and I'm sure other FT'ers do something similar: I keep a spreadsheet for each program, with current and projected trips, miles expected to be earned, including all elite and special promo bonuses. As soon as I book a trip I enter the expected miles from air, hotel, car, deals etc. Then I know what to expect to see, when I look at the online statement summaries, and can easily tell if something didn't post. Don't trust my memory!