Thunderbird is working very slow (often beachball) while avast is enabled. I have disabled the mail modul (because of the SSL errors). Creating and browsing mails in Thunderbird goes very slow.
Another problem: Elgato EyeTV is crashing while closing it: It is only possible to quit the program with the immediately quit the program (CMD+ALT+ESC). Sometimes there is a crash while shutting down the mac like this: http://daniel.cohen.net/blog/2010/04/achieving-nirvana-with-flex-160/mac_os_x_crash/ since avast! for Mac free is installed.
I decided to exclude my Thunderbird profile from being scanned by Avast. I do realize this is defeating the purpose of having a virus scanner. If it wasn’t for the extremely poor performance I would never opt for this as a solution. Think of it as a temporary fix for the problem you are experiencing.
In Avast Preferences click on File System Shield and click on Advanced and select the following path to exclude.
/Users/Username/Library/Thunderbird - replace username with your short name.
I would also exclude where the EYETV is saving data during live recording.