8 out of 10 times roughly when I install any apps on my new mac pro ( I have apple care btw ) I get a standard or weird icon.
I have never had this problem with os x before and I cant understand for the life of me why it does it.
1. Download official app from trusted website ie msn messenger from microsoft or any other app ie disco etc.
2. mount or install app whether it be a pkg or a dmg via drag and drop or double click or w/e.
3. It installs the app which works fine yet the icon view of the app is the weird app icon as per attachment , I know I can fix it by doing a Get Info on it and dragging the image at the bottom to the icon at the top but why is it doing it ?
This is a fresh install of mac os x from the installation discs yet it still does it, yes I did a format before I re installed.
I had a similar problem when I went form Tiger to Leopard, but thankfully it went away after several os updates... I could not find a definitive fix however try force quit and restart the finder Alt-Command-Escape. Its a pain but seemed to do the trick.
A couple of other tricks you could try are
repair your disk and repair permissions regularly
use a utility such as Onyx
oh yes and use Adium instead of MSN
Hope this helps