Yea, I've had that before. I generally shoot Provia, and it has a tendency to scan blue.
I don't use IT8 targets for calibration (I've heard good things though); instead, I generally toggle between "white balance," "neutral," and "auto color" in Vuescan. I have tried doing linear scans with ColorPerfect, but I think it works better with color negatives--I've had mixed results with slides, and it takes a long time.
I essentially try to get as close as I can with the color presets in Vuescan, and I generally mess with the white and black points in order to get as much information out of the slide as possible. Then, I play with it in Photoshop or Aperture. I do all of the contrast adjustments, and then I select a neutral gray/white/black, and that ususally gets it there. I use the slide as reference, but you have to remember that the color of the backlight you use for slide viewing influences your perception of the colors on the slide.