The Google Spam filter is the best I know, hundreds of messages are filtered every day. I have currently over 5000 unread Spam messages in my Spam folder. However, the counter seems to be more important than my inbox counter, which isn't true I hope.
Use the new Tweak UI preferences to hide the spam counter and/or the invitation box. Plus there is a setting to highlight the inbox row that is "under" the mouse pointer.
These new preferences are much inspired by the "Better Gmail" Firefox plugin.
Important: This feature works in Gmail 2 only!