Patty lacks confidence and self-belief in the most important matches.
Since Aus Open 2004 (where she reached the semifinal but without a big win), in the important matches at the Grand Slams, Patty has given poor, un-inspired, under-achieving performances over and over again. And i think it's clear that the reason for this is, Rainer Hofmann is doing a poor job of motivating Patty and preparing her psychologically for these matches. He has basically turned Patty into a player like Sylvia Farina or Maggie Maleeva or Sandrine Testud who were very consistent on tour but always faltered against the big name opponents in Grand Slams.
If Patty would have played with some enthusiasm and fire against Venus Williams at Roland Garros, she would have won that match for sure because Williams was less than impressive in most of the rallies. This was one of the biggest matches of Patty's career, yet in the deciding 3rd set, she looked like she was just going through the motions. In the losses to Mauresmo and Dementieva at Aus Open and US Open, Patty played like a soul-less robot and was simply crushed. At Roland Garros 2005, Patty came in riding a tremendous clay season, got a great draw, and she should have convincingly beaten Mary Pierce and continued on to reach the final. At Wimbledon, viewed by many as the world's most prestigious tennis event, it goes without saying that Patty should have done much better in the last 3-4 years, considering she has one of the strongest serves on tour.
But after each loss, Hofmann has nothing to say except to make some weak excuse and then, two weeks later, print something on his website like "Everything is going perfect for us, we are such a great team, we are working on many problems together and making excellent progress, bla bla bla". Instead of trying to avoid the blame, Hofmann should recognize his own limitations and hire a professional tennis coach, because looking at the results, it's clear that he is not able to give Patty the proper psychological support that she needs to reach the next level at the Slams. In 2002 under Hubert Choudury, Patty was a faster, more exciting, and more emotionally inspired player than she is today - even though she often struggled with inconsistency back then.
Of course, the fact that Patty has reached the Top 10 earns Hofmann some credit, and it's true that maybe with a different coach it won't be any better, but at least they should try to change something while there is still time. It wouldn't take a "Tennis Einstein" to coach Patty successfully. You just have to make sure the strokes are in working order, make sure she is motivated and focused and the rest will take care of itself...