Do you have any files open? Are any served files open in 12?
Nope. As I wrote above, all automatic functionality is turned off (incl sharing, updating etc). There aren't even any files open. The thing should be flat dead.
I have been working with FMP 12 daily since its release, on projects for two different clients (one with a solution converted from ver 11, the other built from scratch). IMHO ver 12 is slower and buggier than most users fully appreciate (or are willing to admit). That said, I suspect the problem you are reporting may not be the fault of FileMaker.
The closest thing I have seen to what you are describing happened a number of years ago when running audio and video editing software on a PC running Windows XP Pro (32 bit version) when 4GB of RAM was installed. When I reduced it to 2GB all these problems went away. System performance was marginally slower, but stable. (Definitely worth the trade off).
I am not saying that there is a flaw in the way that FMP12 uses system resources, just that I have been using it a lot (on a PC with Windows 7, 64 bit version and 6GB of RAM) and I haven't seen what you are describing.
Have you monitored CPU usage for other apps? Have you run diagnostics on your system RAM? Is your OS up to date on patches? I think you may find that some of them periodically ping the OS and spike CPU usage briefly. Or your OS may not be releasing its cache memory. If so, you may be able to rule out FMP as the source of the problem.
Just did a quick check on my MacBook Pro, 10.7.4, 8GB RAM:
FMPA Version / % CPU / Threads / Real Mem.(MB)
12 / 0.3-0.5 / 24-25 / 118.2
11 / 0.3-0.5 / 26-28 / 124.8
For comparison, Word, no document open, no new document open, just "idling" in the background:
2011-14.0.0 / 0.2 / 4 / 61.1
I don't know ... doesn't seem to be "excessive"
Yes, I used to have those problems when I ran Windows OS. Now, I use Mac OS X but I'm pretty sure this isn't an OS thing. All other applications behave well (don't have any Microsoft products though), and unless they have some low-frequency business in the background (like repeated web connections), they consume 0% CPU.
BTW, I've tried the FMP12 on three different machines, and two different versions of OS X, and they all give the same result.
Yes, 0.5% CPU is actually a lot – you shouldn't have to have a dedicated machine to run FMP12, should you? In my case it actually ups to ~1% occasionally. All my other open applications (in Mac OS X 10.7.4 – Finder, Keynote, Pages, Mail, TextEdit, iCal etc…) use 0% CPU. Although I don't have any Microsoft products like Word or so, I believe a proper application behavior is to idle down to 0% unless there is some occasional background activity needed.
Both for efficiency reasons and security, this really bugs me. Wonder how much extra juice this beast sucks when it's actually doing some work, like serving data?