I'm not so sure about that anymore. Derrek Lee is borderline useless. He still is a solid defensive first basemen but he can't hit at all anymore. Cubs leaderboard by OPS, at this date last season:
Name PA OPS
Lee, Derrek 100 1.130
Soto, Geovany 82 1.069
Ramirez, Aramis 98 0.996
Cedeno, Ronny 37 0.995
Fukudome, Kosuke 91 0.986
DeRosa, Mark 87 0.877
Theriot, Ryan 83 0.871
Blanco, Henry 16 0.795
Johnson, Reed 71 0.755
Ward, Daryle 19 0.676
Fontenot, Mike 36 0.575
Pie, Felix 37 0.529
Soriano, Alfonso 61 0.528
Murton, Matt 10 0.200
Patterson, Eric 6 0.000
It bears SOME resembalence to the end-of-year leaderboards, of course. But last year around this time, everyone was freaking out over Soriano. He ended up the season with typical Soriano-like numbers. It's way too early for people to be jumping to conclusions like that. Lee hasn't had a month with a .800+ OPS since the first month last year. That's a span of 141 games and full calendar year. Lee is simply no longer a good offensive first baseman. He is however still a good defensive first baseman which is why I think he is still starting every game.