I just did that a couple days ago, along with all the ST2.5 libraries. Haven't tried the Miroslav content yet, but I was disappointed to find some of my favorite ST2 patches didn't make the transition.
 
ST3 crashed three times during the import, until I broke it down into smaller chunks. Then I ended up with duplicates and can't figure out how to delete them!

Better open a case with Support, they respond very promptly.
For me, importing Miroslav and SonikSynth went smoothly, except for one file in SonikSynth I had to remove first.