I have a user who uses the sql variant data type. Currently the database he uses is read only and he has noticed a lot of "garbage" in the column in the last few days. A dbcc shows no corruption and the user is following the rules of the sql variant data type as far as we know.
One last thing, he never had this problem on AS 2000.
No, but I guess it does not surprise me that there could be miscommunication between applications or utilities when exchanging the SQL Variant data type. I would avoid using it except for certain functions or procedures that might need to act on unknown datatypes. The fact that you have it built into your business logic makes me suspicious of your design. You certainly do NOT want to use it as a "default" datatype for all your columns.
If it's not practically useful, then it's practically useless.