You probably know that one of the cool new features of the Content Query Web Part in SharePoint Server 2010 is the support to QueryString and PageField filters.
This was achievable also in MOSS 2007, but you had to rely on Parameter Bindings applied to the CQWP control, which made it a little more complicated since it requires some more knowledge about the “DataView family”.
Just a small note, though: if you keep using the QueryOverride mechanism (i.e., you specify a custom CAML query overwriting the default CQWP behavior), you completely lose the new filters functionality.
More generally, any time you apply some override (Query, View, etc…) the CQWP skips its automatic CAML query/filter/projection generation, and all of the plumbing it’s up to you.
With great power comes a great reponsibility!!