The maximum number of target buckets is either 1,000 or 10,000 depending on the version, you can confirm which you have using the following:
SELECT name,max_val FROM pg_settings WHERE name='default_statistics_target';
Setting an extremely large value here does incur overhead on every query that is planned, and, as mentioned before, just the increase from 10 to 100 measurably detuned the trivial query runtime in PostgreSQL 8.4. There are however some table columns where it takes substantially larger settings to get sufficient statistics about the data to make accurate estimates. It's not unheard of in a large data warehouse setting to increase the target to 1,000 or more to sample enough of a giant table to represent ...
