I've had the same problem noted above since yesterday. When you select the Yahoo option to add your account (via the stock app), it pulls *ALL* of your emails into the same inbox. (Seriously. Is this like 1998?) You have the standard folders (inbox, sent, trash) available to you, but the custom folders are not imported and synced.
Conversely, the other alternative is to manually add the Yahoo account (select "Other" when prompted to choose). It took me the better half of the afternoon to even find the correct settings online so that it would connect, but I finally figured it out. (Incoming: imap.mail.yahoo.com // 993 // SSL/TLS // Auto Outgoing: imap.mail.yahoo.com // 465 // SSL/TLS) After the lengthy sync process finished I was excited to see the custom folders, but I can't get Yahoo sync when configured that way. (Yes, sync was turned on and set to pull every 15 minutes).
I'm fine with the fact that Yahoo doesn't push the emails; that was the case with Gingerbread. But I can't deal with no sync whatsoever.
So now I feel like I'm stuck choosing between the lesser of two evils - no sync or no folders. Would gladly take any suggestions.!