Some 4 years back, I followed this MSDN article for DateTime usage best practices for building a .Net client on .Net 1.1 and ASMX web services (with SQL 2000 server as the b
I think the best way of doing this is to always pass the object as UTC, and convert to local time on the clients. By doing so, there is a common reference point for all clients.
To convert to UTC, call ToUniversalTime on the DateTime object. Then, on the clients, call ToLocalTime to get it in their current time zone.