Using XP.
AVG was expiring and I purchased Norton Internet Security 2010. Removed AVG and loaded Norton in on Sunday and Monday immediately noted that my computer was slower. There were unusual delays when I either tried to open a folder in My Documents, clicked on an icon, tried to delete a file, or tried to save a file. I was repeatedly getting Not Responding error messages. After frustration for several hours, I removed Norton and downloaded AVG, which I am now using.

The long delays are gone, though there is still some isolated sluggishness. I would estimate that I am probably 90% back to where I was before I loaded in Norton.

All due respect to those who have Norton and love it, but for me it was a disaster. It may be a long time before I try another Symantec product.