Delta’s transfer miles page shows a 50% bonus for moving miles from one account to another (at a cost of a peny a mile). When you click the link to the offer it takes you to the page from the 100% transfer bonus offer which expired December 16th (and was actually pulled at the beginning of that day rather than the end, blocking my plans to take advantage of the bonus at the last minute). So we don’t know how long this one is scheduled to last.
I won’t be taking advantage of the 50% bonus. While I think that a 100% bonus offer is a great opportunity to effectively buy miles at 1.1 cents apiece, and despite all of the drawbacks of Delta Skymiles (I’m the person who coined the term Skypesos, after all) they’re certainly worth a penny apiece when used for Air France business class for instance, there are plenty of things you can do to maximize value of the points. I don’t think that a 50% transfer bonus, effectively buying Delta miles at twice that price, is worthwhile.
Some will find it useful to clear out orphan points, especially to top off towards a specific award. But without a defined redemption pending, and since Delta miles don’t’ expire, I’d wait for the return of a 100% bonus to return before jumping on the offer.