YESUAINI99  avast for Mac Edition keeps crashing when I scan the entire HD.

Also, find it impossible to find any documentation on how to uninstall it.  
(Version 2.74)

PIRX  In general, in the Windows world Grisofts AVG found at least 6 more infections on our office machines than Avast did.

For Mac, I was looking for an AV that scans the single biggest source of infection: e-mails. I do forward e-mails, so passing on Windows infections is a possibility. Avast plugs into your Mail.app and launches it. If you uncheck the mail option in the preferences, no mail scanning seems to be happening. Apart from my preference to launch my e-mail software at my leisure, Avast completely ignores the fact that many people do not use Mail.app, but things like Thunderbird, PowerMail, Entourage, et al.

So, in terms of what I really wanted to have, e-mail scanning, it does not perform as expected.

The HD scans are fast and thorough, no complaints about that. No crashes or hanging on OS X 10.4.11.  
(Version 2.74)

ALTERO-TOT-EU  avast conflicts with Mail.app.

Do not install it!  
(Version 2.74)

HELIOS9  While it's got an easy to use UI and seems to be quite thorough(I ran it but no "cooties" were found on my hard drive), be aware that Avast Antivirus is not for purchase; you buy a license to use it for one, two or three years at a time.

Currently, a one year license costs $40, a two year license costs $58 and it's $74 for three years.

The Avast company is Czech, and heretofore has sold most of their software to European buyers, so most likely, their antivirus software licenses will become more and more costly for those of us in the States as the dollar vis a vis the Euro loses value.

So Avast Antivirus is quite expensive to use, especially if one expects to use it for a number of years.

One irksome fact is that their antivirus software for Windows(their home edition used non-commercially, has FREE yearly licenses, while we Mac users have to pay for them! Most puzzling, since Windows is just plagued with viruses/malware while there are, as yet, NO active ones out there for Mac.

I, for one, will pass on this one; I'll just continue to use the free and highly regarded ClamXav.  
(Version 2.74)

IMHO  Downloaded avast! -that I already knew from the Windows platform - yesterday and scanned my Mail- and Downloadfolders. avast! found eight infected files, all .exe files. Looks as a real Mac-program and I liked the built-in manual. Seems to work rather quickly.  
(Version 2.74)

COMPLEX_PERSON  I have my parents PC using Avast anti-virus, it works well and is completely FREE for home use.

Where's the FREE home use for the Mac users?  
(Version 2.74)

RPPHOTO  Looks pretty, but it's funny: the first WARNING I received while running it was for something called "Avast!.app"!!! So far it's only about 1/3rd of the way through its ritual, and so far that's the only warning... .

Hope that's not a bad sign; it would be nice to find a good app like this since at some point in the future we'll need this...  
(Version 2.74)

ROY VAN DER WONING  Perhaps the developer can provide some independent reports on "the ever-increasing malware threats being deployed against the platform"? I miserably failed to dig up anything substantial in this area.  
(Version 2.74)