First off this post does not only apply to 2010, it also applies to 2009.
In RAC & RME filters can be applied to elements according to parameters associated with that element or elements. When you select the Filter tool you are presented with this dialog.
You choose a parameter, a condition, which element(s) to affect and name it. In Visibility/Graphics you can add the Filter to the view. Once added you can alter the appearance of the affected elements or even turn them off.
In RST filters do that AND you can build selection sets and use those as a filter too! When you start the Filter tool in RST you get the dialog hiding behind the foreground dialog. You get this foreground dialog when you click NEW.
So are you getting annoyed yet? With RME we use filters extensively to manage the appearance of duct and pipe according to the system they belong to. With RAC we use them to alter the appearance of plans for "FFE" (Furniture, Fixtures & Equipment) requirments and fire/life safety documentation to name just a couple.
Imagine you could build a filter by just selecting a number of elements instead? Select this, that and the other thing over there...okay now you are part of a filter and you can do all the same override stuff!! Very nice!! When you enter into the "Select" mode you get a new contextual Ribbon tab that looks like this.
Similar to Groups you can add/remove elements from the Selection Set. I did notice that the Filter tool isn't available while in this mode. This makes the Multiple check box on the Options Bar a bit anemic since you can't use Filter to remove a category of elements after using a crossing selection window. But then maybe getting to use the Filter tool while using the Filter feature would be "redundant"?? If so I'd have to post this in my Dept. of Redundancy Dept.?
I have to ask the obvious question...does someone think that Revit Architecture & MEP couldn't use this feature too? That said, I believe that this is the "Selection Sets" extension that was released for RST in past years getting incorporated into the native code of RST. It's a shame that it isn't in the others. Perhaps next release!?!