Mypoints => HHonors: 1,000 to 1,000
Mypoints => Marriott: 1,500 to 1,000
HHonors => Delta: 50,000 to 12,500 (current 25% bonus promotion, see
http://www.flyertalk.com/forum/Forum57/HTML/001209.html )
Marriott => Delta: 30,000 to 10,000
50,000 Mypoints would become 12,500 Skymiles (4:1 transfer through HHonors).
45,000 Mypoints would become 10,000 Skymiles (4.5:1 transfer through Marriott).
[Edited to add link]
[This message has been edited by Eugene (edited 02-16-2001).]