Shadows is an old hiden feature, but it seems shadows are more stable in the new viewer.
As an SL/Rl architect said last week ..."For the longest time, I had given up on the possibility of using shadows persistently in Second Life, given that it crashed my viewer so often it wasn’t worth the hassle. But since enabling shadows in the new viewer 2.0, I haven’t crashed yet!"
Mmmm i have test it and i crashed again lol, but it depends on hardware configuration...so you may try it!!
KirstenLee Cinquetti started to included shadows in her SL viewer seince 2008 and now she has build one of the best SL viewers (if you want to try go to her webpage http://www.kirstensviewer.com/).
Look this nice article talking about how activate dinamic shadows in Second Life....
http://nalates.wordpress.com/2010/02/27/second-life-viewer-2-0-beta-review/
