She has a few problems:
1. Maria Sharapova--this is an aweful matchup for Venus. Maria hits harder and more consistently than Venus, and runs much fast enough that Venus can't smack winners on the run like she can against, say, Lindsay.
2. Lindsay Davenport--this is always a tough match for both. Lindsay controls the points most of the time. When Venus had LD's number, it was because Venus would smack away winners from defensive positions. LD isn't explosive (her footspeed actually isn't that bad, but she's not quick out of the gate,) and therefore can't change direction and run for a ball that she didn't expect. However, she's worked on that a bit, and Venus has slipped a bit.
3. Venus Williams--Venus is still a hazard to herself. Even when she's playing well, her technique is so shakey that she can go off. This is not 2000/2001. Players hit harder and more consistently, and will take opportunities given. Back in the day, Vee could afford her 3-4 game mental lapses. Today she can't.