Certainly. FCP X uses a lot of RAM. As does Aperture (they can both use multiple GB of RAM). Which is fine; the whole reason 64-bit applications can be faster is they can address > 2 GB of RAM in their process, which can make some things faster (videos and photos take a LOT of RAM to edit).
Memory usage is pretty complicated. There's a lot that goes on behind the scenes to optimize the performance of individual processes, as well as the performance of the computer as a whole. And the trouble with tools like Activity Monitor is that they're only giving you a coarse view of what's going on.
I'd suggest you don't be alarmed, and in fact don't even pay attention.
Here's really the only guideline I'd pay attention to: If you open up the System Memory tab and you see the "Page Outs" number growing, then the system is paging and needs more RAM. At that point, I'd recommend you close down some applications, and the system will reclaim the RAM it needs to. Rebooting frequently to keep the numbers low isn't really helpful, again because inactive RAM can be faster than active RAM if you re-launch an application.
One note I'll make: I used to use a program called iStat Menus to track memory usage. In a couple builds it had a HUGE memory leak to the point that my kernel_process was memory mapped to something like 164 GB of RAM (on a system with 12 GB of RAM). So a COLOSSAL leak. The tool was causing problems in the things it was attempting to measure! Even then, that stuff was mostly paged out and the system wasn't much slower, because it wasn't _actively_ paging. I uninstalled it ;-) They since fixed the bug, I think, but honestly it's not really worth worrying about, unless the system is paging a lot (and with 24 GB of RAM, it shouldn't be, almost ever!).
