Adding TEXT columns tanks performance?

Hi all,

Saturday I changed a table to add a varchar(24) and a TEXT column.
It's used for some reporting purposes (small potatoe stuff really)
and the TEXT column remains mostly empty.  However, this week
performance has gotten terrible.  Queries joining against the
aforementioned table have gone from 40s to 1500s.  The schema change
is the only explanation I have for the 30x slower queries.  The
queries have definitely gotten disk-bound (I can see the connection
process sitting in the D state for several minutes).

This is pg8.1.4 on Linux RedHat. Would adding a TEXT column impact
things that much?  The change to the schema was

alter table foo add column title text;

tia,
arturo