I haven't ever played with "Upsampling" and I'd like to.
 
Before I re-invent the wheel though, is there a list anywhere of effects/instruments that people know definitely make use of and benefit from the function? Is there something that you found upsampling made an audible difference with?

this was a good topic here. haven't dove in to US either yet. but it has many benny's
http://forum.cakewalk.com/Plugin-upsampling-in-Sonar-my-experience-so-far-m3386790.aspx
 

Read through that a few times :-)
 
I'll be honest, for the life of me I can't find anything that I hear a difference on. Even with my higher end headphones.