Screen captures in Panther may appear blurred because they have non-square pixels. If you take a screen capture with Shift-Command-3 or Shift-Command-4, then open the PDF screen capture file in Photoshop CS, it will have a pixel aspect ratio of a tad more than 1, and your image will be slightly blurred unless you turn off Pixel Aspect Ratio Correction. Don't open these files in Photoshop 7 or earlier, as there's no option for correcting the pixel aspect ratio and they'll go soft-focus. Also, don't copy a screen capture to the clipboard (e.g., Shift-Command-Control-4), then paste it into Photoshop, because Photoshop will re-rasterize and blur the image (I presume the clipboard file format is PDF).
For sharp screen captures in Panther, you could also use the Grab utility. Unfortunately, it's more hassle than the direct-to-the-clipboard method that worked properly in Jaguar, but at least there are workarounds for this bug.
[robg adds: I don't have Photoshop CS, just Photoshop Elements 2.0, and I don't think this bug is Panther-related ... or if it is, it's not obvious in Elements. I took a number of shots: (1) Direct to clipboard, (2) via Drag, (3) Using SnapzPro (saved as PDF), (4) Shift-Command-3. I then put all four images on top of one another in Elements, and the various widgets seem to line up perfectly, and nothing looks blurry -- here's my .psd file, if anyone wants to take a look [369KB download]. So either they're all 'blurred' the same amount, and I'm just not seeing it, or they're all fine ... anyone have any more info on this possible glitch?]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040204205840385