I just upgraded a clients' pix from 6.0.1 to 6.2.2 sw and just for kicks, we went to a few online scan services such as grc and sygate to run a few scans against the PIX. Prior to the upgrade, any port showeed up as stealth or blocked. After the upgrade, we ran the tests again and the ports showed up as "closed".
Granted, many online tests have to be taken with a grain of salt per their results, but still, it was quite shocking to the client. I rolled the pix back to 6.01 and re-ran the same tests, now they come back as stealth or blocked.