I've been working with the ArcGIS Server Release Candidate 9.3 REST interface - pretty slick, I must admit!
However, the documentation is pretty thin as of now.

So, for those of you out there wanting to specify a date or date range in the WHERE CLAUSE of an ArcGIS Server REST Request, here's the skinny:

//Javascript - assumes you've got a Javascript Reference pointing to the ESRI Google Maps Javascript Extension

var _query = new esri.arcgis.gmaps.Query();
_query.where = "MyDateColumn >= date ’01-01-2007’";

This would give you results with a date matching after January 1, 2007.

More with the ESRI ArcGIS Server Libraries to follow!