Reified generics is one of the reasons why Scala on the .NET is effectively dead. The VM's type system isn't powerful enough to support some features of Scala, such as higher-kinded types.
But the JVM not having reified generics is a mostly a blessing for Scala. With reified generics, your language's type system can essentially be only as powerful as the VM's type system, and I think it's clear that Scala today wouldn't be the same if Sun had gone the reified generics route.
(Still, it would be nice to have specialized generic containers for some primitive types in the JVM)