I am also having problem with WP Stats since my upgrade to 2.3. It keeps asking me for username and password every time I check my stats, even I checked "Remember Me" option. Also, Stats displays the post Id instead of the post name, and the link is pointing to the wrong place.
Another thing is when I login to WP Stats, it loads up my WordPress.com account's global dashboard inside of my blog's dashboard, and I have to click the "Blog stats" within the global dashboard to see my blog stats. Very annoying!
I worked very well with WP 2.2 until I upgraded to 2.3.
Can someone help? There is a Trac ticket for this issue, but it has been marked as Invalid, I can't believe it.