I don't think the most important reason why Pirlo is very sucks in 2006 is all of himself. I think there are 3 important reasons :
1st, Ancelotti didn't give him enough rest. Vogel is not bad but Ancelotti still uses Pirlo which makes us very strange !! Compare last 3 seasons, sometimes Ambrosini or Redondo even Brocchi have some chances as a DM, but this season Ambrosini always injured, his health body can't keep more than 3 weeks + Vogel doesn't play a lot of games ( I think sometimes when we VS a weak team we can use Vogel ).
2nd, our competitions always uses 2 or even 3 players annoy Pirlo ( I think most of yours know O'Neal, the basketballer of Lakers, he is very huge + strong, so sometimes other teams use 2 or maybe 3 players annoy him ), i feel our competitions annoy Pirlo likes the baskerballers annoy O'Neal.. But O'Neal is strong so sometimes he is no problem. while Pirlo is weak + slow, it is easier to annoy him ( Especially for some dirty players !! ).
3rd, our defenders and midfilders lack enough help to Pirlo. In last 3 seasons, Gattuso only need to protect Pirlo, but in this season, Gattuso has more attack ( he had 3 goals and 3 assists, it is very excellent compare him with last 3 seasons ). And our LB usually uses Seriginho, although his defense ability is a little better than last year, he is still very weak at defense, last 3 seasons we use Kaladze or Pancaro, their defend are solid enough ( although weaker than Maldini and Nesta ), much better than Serginho !! So the problem for Pirlo is he is a DM, without Gattuso's protection + need to help Serginho defend, that makes him more tired !
And i find a lot of guys say we should sell him or someone say he is an idoit, i disagree with them, Pirlo is still an important key-player for us. We should know we are lucky because we have him. Maybe he would prove himself in Italy ( Because Italian defenders + midfilders can help him more ), so if he has good performance in Italy and even help Italy get good in WC, i hope Ancelotti can think carefully, give him more support, i hope Pirlo will repeat 2002/03 and 2003/04.