Are indexes blown?

Hi,

I have an index on the user_id field in the query below:

   myuser=# delete from clients where user_id like '64.22.91.%';
   DELETE 22
   Time: 220324.975 ms

Is there any reason why it's taking 220 seconds to run this simple
query? There are about 3 million rows in this table.

How can I debug this? How can I check if the index is bloated or
blown? From the VACUUM ANALYZE output, nothing like this is apparent.

Thanks.