Hallo,
> If I receive an infected file (download, mail, etc.) and the GUI is NOT running, would I be warned or infected?
mails are scanned even when the GUI is not running. after-close events (= on access event) need the GUI-application running.
> The confusion also maybe because the GUI starts up every time I start my Mac.
in the fact, the main part of avast's engine works in userspace on all systems, so there must be always some mediator that relays the kernel-level events to the scanner. on mac, the userspace queueing-halve of this mediator lives inside the gui application. indeed, the GUI's auto-pop-up after login might make weird impressions for some users, like "why must I run some app to get the background protection?". But, it's always necessary to run some userspace app anyway, and it's only matter of better/worse hiding. New hidden mode will be added to the next release.
> That seems to be a bit excessive. I'm not sorry that I bought avast! for the Mac, I just thought it would work similarly to the PC version or other Mac virus apps.
Such memory consumption might be normal, the virus database itself takes about 17MB, + all runtime mapping structures, + transaltion buffers, you will end up somewhere near 30 MB. Please don't mix virtually-alocated memory with resident-shared-size, in my case (the worse one - PowerPC), after scanning my crowded homedir, the daemon takes 22MB RSS only, and the GUI, with full list, 14MB. That's not that much, but still, we'll do our best to minimise the memory consumption any farther. In general, PowerPC engine differs from the PCish one in size (cca +1.6MB - RISC codes tends to be more bloated than CISCed x86) and also in runtime memory consumption (+ 8MB for specific runtime translations), that's 30%...
Regards,
PC