Photoshop and Aperture are different programs for different
tasks. Lightroom and Aperture are closer. On Mac I would suggest
Aperture. Especially new version 2. Powerful tools to adjust and
correct images. Integration with all programs: iPhoto, iLive,
iWork. Smart folders, Light Table, books, web, slide show
publishing. No restriction on where images were saved. There are
videos on Aperture web page. Interface is up to personal preferences. I
recently switched to Mac and from Lightroom to Aperture.