Avast did not automatically add itself to the login items on Leopard (Intel). So I had to manually add it to have avast launch at each bootup.
Hmmm, this effect isn't Leopard-related only (occurs, for example, on a freshly installed Tiger too *). Unfortunately, this functionality (~ adding to LoginItems by a "third party, non-preferenced" app) isn't officially supported nor recommended by Apple (according to OCS, Apple states "This is not done."). Some applications use a half-dirty trick how to do this (Apple posted this "hint" to some developers who requested this functionality), and we did it basically using the same method. We'll try to workaround this case.
* after addind anything (even temporarily) to LoginItems, the whole mechanism starts to work since this moment. that's why nobody noticed, because avast! isn't usually the very first application that we have installed.