It appears the April 2008 Rosario CTP is now available.  Per Jamie Kurtz's blog:

This seems to be CTP12: http://www.microsoft.com/downloads/details.aspx?FamilyID=65D0E3BD-9DF3-421A-804F-8F01BD90F0B4&displaylang=en

And here's the Free Download Manager list:

http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part01.exe
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part02.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part03.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part04.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part05.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part06.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part07.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part08.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part09.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part10.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part11.rar
http://download.microsoft.com/download/b/f/9/bf9c1b30-ca2d-4381-8e9e-8b5db9701437/Apr2008RosarioCTP%20_12PartsTotal.part12.rar

Thanks Jamie for putting that together for us.

Update:  Jeff Beehler has some good information on it as well.