A quick sample of usage as requested by my friend Jeff McWherter:
Querying for all data in a table where the "zip code polygon" is within 20 miles of a geocode point (must convert 20 miles to meters in the predicate)::
select *
from dbo.fe_2007_us_zcta500
where Boundary.STDistance('POINT(-79.8884595930576 43.2609696686268)') < (20 * 1609.344)