Because of how generics are implemented in Java (eventually compiling down to objects and casts), what are the benefits of using them?
Should I still use them for the compile time type safety? I'm used to the significant speed boost of generics in C# and I'm curious if people who work with Java still frequently use generics despite their implementation?
The compile time type safety is important enough that I believe it warrants using generic arraylists, so you should use them, IMO, as I don't generally see a good reason not to.
It helps to let other developers know what you are storing in there, and the auto boxing/unboxing is very useful if using primitives. It simplifies the coding you have to do, even though it is more work for the compiler.
The benefits of using Java generics are purely that your code is less cluttered with casts, you are able to state your intentions at compile-time about what your collections can contain and have these intentions checked by the compiler.
Java generics have nothing whatsoever to do with performance. As James Black says, because in Java, generics are erased, there is no difference at runtime between Java code which uses parameterized types and Java code which uses raw types.
So yes, we still use them because they make our code clearer
EDIT. I seem to have been downvoted because I did not realize that you were talking about the ability in C# to have a collection of primitives (what with them not actually being mentioned anywhere in the question): e.g.
List<int>
If I really care about performance (i.e. squeezing every last microsecond from a Java program) then I'd use an int[] array and, yes, it's a shame that Java doesn't have primitive-collections. For most programs, I don't think that this is a real issue, however, so I'm happy to use List<Integer> in Java for its added convenience.
Yes, you should use them for the improved type safety. By using raw typed collections, you are following an old code path that was only kept around for compatibility.