Just a heads-up to those who, like me, built their family tree on ancestry.com and wish to export it to family tree software such as FTM2010, RootsMagic4, et. al.
Ancestry.com GEDCOM export is, as of the time of this writing, broken. It will export all of your data but some will be misplaced and more will be unlinked. This can be repaired but it's a real chore. Here's what I had to clean up manually in mine to make it compliant with LDS's own standards:
* Unless you're using FTM2010 or you don't mind the LST file errors remove all the _APIC entries. They're harmless but generate a ton of warnings.
* Look for MARR entries with import errors. These will invariably be associated with an individual (INDI) record rather than a family (FAM) record. Cut the MARR entry from the INDI record, find the FAM record that has the INDI record's @******@ ID number as HUSB or WIFE (whichever is appropriate) and paste the MARR data into that FAM record. Find the other spouse and remove the MARR data from their INDI record as well.
* For some reason ancestry.com exports all the sources and all the citations that use them but many of them are left unlinked, i.e. citation notes SOUR @S12345678@ but the source is labeled @S-983458964@ in the data below (note the hyphen in the ID, this appears to indicate an unlinked source in the gedcom). To fix these, find an unlinked event source (from the LST file), inspect the data connected to it and find this event in the online Ancestry.com tree to find the name of the source, e.g. "London, England Marriages and Banns, etc. etc.". Look for that name in the @S-*****@ sources in the GEDCOM and you'll likely find one. Double check the info associated with that source, make sure it aligns with the unlinked event source from the LST file. If it doesn't match up, keep looking. If it does match then pick either the @S-*****@ ID or the unlinked @S12345678@ id and replace the other so they all use the same ID.
WARNING: Make a backup of your GEDCOM before you begin. I re-imported mine after each big fix to ensure that it actually worked and that no new errors appeared in the LST file. It took hours to fix mine even after I had a pattern down. Make lots of backups as you go. A mistake can be very difficult to fix if you can't go back to a previous version.
I hope this helps others running into the same issues. I hope even more that ancestry.com makes this critical feature of their service work properly. After all, GEDCOM is an LDS-created "standard" and ancestry.com is an LDS service...
Had I known when I started creating my tree online what I know now I'd have just started in an offline software package instead.