Everyone's chiming in with "you should always use 'this' because it's more explicit", which I personally tend to agree with. But there is a dimension to this that may not be obvious to people who don't come from Java/C#: these languages don't have non-member functions or variables. So if you're accessing a variable without [obj]. it's either a member of the current object, or it's a local variable in the current function. If you call a function without [obj]. it's unlikely (maybe impossible? I'm not certain) that it isn't a method of the current object. On top of that, by idiom Java and C# code tends to be dramatically more verbose than many other languages. So I could understand the desire to cut that down some when there would also be less ambiguity than in, say, JavaScript.

Edit: @masklinn pointed out the static imports feature, which allows you to import static methods in a such a way that they don't have to be prefixed with the class name when calling them, so I take back what I said about function calls