I worked at a computer store in Vancouver and I personally witnessed the 'unmasking' of 2 PII '300's that were actually overclocked 233s. The alterations were being done at the distributor level and when the situation was reported to Intel they threatened to revoke the distributor's reseller liscence.
Earlier this year, I was upgrading my boss' system (I now work at a cybercafe) and lo and behold, another remaked 233 sold as a 300. I think it was pretty common with the PII 300s

-Ross