vordmeister - 6:23 pm on Jul 27, 2010 (gmt 0)
The initial worries about vB4 were the change in pricing structure and the rush to release that led to a lot of bugs. Those seem to be gradually being sorted.
Apparently styles in vB4 are difficult to modify, it is database intensive and slower than vB3 (though Shawn Hogan has published modifications to improve this), and it doesn't support IE6. vB3 has advantages over vB4 for many.