Extremely slow DELETE with cascade foreign keys

Hi, I think something changed recently in my development environment as
I don't recall deletes being so slow before.

I've created a new dump and restored to a new database, ran VACUUM FULL
ANALYSE and a simple delete takes forever as you can see here:

explain analyze delete from field_values where transaction_id=226;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 Delete on field_values  (cost=0.43..257.93 rows=481 width=6) (actual
time=367375.805..367375.805 rows=0 loops=1)
   ->  Index Scan using index_field_values_on_transaction_id on
field_values  (cost=0.43..257.93 rows=481 width=6) (actual
time=0.223..4.216 rows=651 loops=1)
         Index Cond: (transaction_id = 226)
 Planning time: 0.234 ms
 Execution time: 367375.882 ms
(5 registros)

Time: 367377,085 ms (06:07,377)

Any ideas on what could be causing this? Could it be an issue with my
hard drive?

There aren't that many records to delete from the other tables
referencing field_values. I've done this sort of operation earlier this
year and it was quite fast. Any clues?

Thanks in advance,

Rodrigo.