Hot Standby - ERROR: canceling statement due to conflict with recovery

I have a hot-standby instance setup using Postgres 9.0.1 with streaming
replication against a 9.0.1 master. On the master, I have the following set
in the postgresql.conf:

checkpoint_segments = 3
checkpoint_timeout = 1min
checkpoint_completion_target = 0.5
max_wal_senders = 3
wal_sender_delay = 200ms
wal_keep_segments = 1440

According to pg_controldata, everything is working on the standby:

Database cluster state: in production
pg_control last modified: Sun 27 Feb 2011 12:28:07 PM CST
...
Current wal_level setting: hot_standby

Unfortunately, most queries against the hot standby fail. Worse yet, pg_dump
fails:

pg_dump: SQL command failed
pg_dump: Error message from server: ERROR: canceling statement due to
conflict with recovery
DETAIL: User query might have needed to see row versions that must be
removed.

I'm not entirely certain I understand why I'm seeing this. Nor do I
understand how to fix or work around this. Any advice or suggestions would
be greatly appreciated.

-Sean