Duff Wilson, a developer of Family Tree Maker, emailed me to offer his help. I loaded my FTM 2012 file into my public Dropbox file, and sent him the link to the file on Tuesday afternoon.
His people worked on it and on Wednesday morning, Duff emailed me with this:
"We were able to upload and sync your tree successfully, and the process took just under three hours here in ideal conditions (uploaded internally with super-fast connection). My guess is that it would likely take longer for you depending on your Internet speed. Keep in mind that upload speeds are always much slower than download speeds. In your case, did you let it continue or did you stop it after a couple of hours? Your tree is very large, not only in terms of people (~41K), but also in terms of other supporting data such as sources and citations. It’s hard for me to predict how long it might take for you to upload & sync your tree from where you are, but my guess is that it could take between three to six hours. That isn’t only the time to upload your file of course, but includes the time to actually create the tree online and link it to Family Tree Maker.
I took the screenshot above after I did a little editing, I guess, because it says "Sync needed." I did have four Media items that didn't sync for some reason, and don't know how to find out.
Updated: 1:15 PM: I clicked the link for the Media item problem, hit the "Retry" button and after several minutes the problem went away. i'm assuming that the problem Media are now in both the FTM database and AMT, although I have no way of knowing which ones they were. I'm currently "In Sync."
The "Randy Seaver's Genealogy Database - August 2012" is now a public Ancestry Member Tree (http://trees.ancestry.com/tree/45964539/family?fpid=6454448177):
I edited the "Tree Settings" page a bit also: