I've just made a small modification to SM and the SMLoader - you can 
get my versions from

http://beta4.com/mc/SMBase-avi.43.mcz
http://beta4.com/mc/SMLoader-avi.9.mcz

This adds #defaultRelease to SMPackage, which finds the last published 
release if there is one, otherwise just uses the last release of any 
kind.  The SMLoader uses this when installing a package with no release 
selected, and it's also used to determine the #smartVersion of a 
package.

I'd really like this to be integrated so that I can feel free to 
release alpha versions of my packages without worrying that people will 
install them by accident.

Avi