I haven't noticed it said yet but the biggest issue here is memory aside from the Intel emulating the PowerPC issue.
If you can get at least another 512MB to bring you up to 1GB that will help a lot as it will let the Mac 'breathe' a bit better. Macs are pretty memory hungry in the initial phase but become more efficient over time—if that makes sense.
Ie: Your mac ideally needs 512MB to wake it up in the morning and if you give it that it will eat it all, greedy little thing that it is! If you have 1GB though, it may consume a good half of that but anything you run afterwards will run very efficiently (memory does not seem to disappear)
For example, I'm using the Power Mac listed below—and presently have OS X Tiger, Safari, Mail, Preview, iTunes, Adobe Photoshop, Illustrator and InDesign CS2 running and out of the 1.5GB RAM I have 540MB free RAM—which is pretty goopd considering all the CS2 apps have documents open.
My advice is invest in a good wodge of memory—emulation takes a lot; presuming Rosetta uses JIT (just-in-time) translation of PPC->x86; then it will need a lot of memory, lean JIT compilers tend to require 4KB for every 1KB of PPC code; so when that is multiplied up you can see heavyweight apps will literally devour RAM and then eat into other areas of memory, namely virtual memory page files; resulting in the Mac copying chunks of code from RAM into VMEM and vice versa—on top of the strain of emulating a PowerPC G4 processor.
Yes, it does *not* emulate the PowerPC 970 (G5) series as it only emulates the PowerPC 603e+AltiVec instruction set or what we call the G4...
More information behind the Rosetta technology is here:
http://www.transitive.com/
Anyway without getting off the beaten track, sadly the Intel Core Duo will be throttled when emulating any PowerPC app and aside from going to a PowerPC based Macintosh the only way to really get any decent speed gain until native apps arrive is to boost the iMac's RAM as high as you can.
Vicky