I don't think that they'll overtake Nintendo or Microsoft in this generation in the US in terms of lifetime console sales.
While they're close to MS by a decent margin, and they may overtake them in the short term (month by month) once the gap in price difference between systems normalizes, they're too far in the hole since launch numerically to pull ahead. It'll be a shock to me if they overtake MS long-term and a downright impossibility for them to catch the Wii.
What I DO think that they're absolutely capable of doing is beginning to manufacture a profitable system and over the course of the next 6-7 years (or however long they keep the unit in the market) make up for the money that they've willingly lost in the early years of hardware sales.
Remember, Nintendo trailed in console hardware sales last gen, but avoided bleeding money in the manufacturing costs ... they wound up rather comfortable (healthy DS and GBA sales notwithstanding) despite coming out in last pace with units sold.
Microsoft are going to be in a hole financially from hardware sales this gen due to the reported billions already lost in extended warranty/repair/re-design/replacement programs.
Sony is very good at re-designing hardware to minimize cost - PS1, PS2, PS3, and PSP have all seen numerous hardware profiles specifically designed to lower the production cost of the unit, and Sony has generally done an excellent job of passing along those savings to consumers.
Again, I see no reason why a profitable PS3 in the market for the remainder of this console generation isn't possible. Sony is trailing but they're healthy enough to stick it out and make the best of it.