What is the advantage of the dyneema over wire? Easier to make, lighter?

The one disadvantage i can see is rope is prone to tangles and nasty knots.

And Steve have you ever had one of those series 20 ronstan blocks fail? I found the stainless steel strap gets bent then gets deformed. Ive never had one break on me but it completely stuffs the pulley. Might have something to do with the losds i'm putting it under! I ended up used the RF30100 http://www.ronstan.com.au/marine/product.asp?ProdNo=RF30100 .