explicit JOIN faster than implicit?

I'm in the process taking a large SELECT statement which had been
written using implicit join syntax (that is, just listing all the tables
in the FROM clause, and listing join conditions in the WHERE clause) and
rewriting it to use explicit JOIN syntax (they are all inner joins).
This has sped up the query by 50%.

This is using Postgres 8.3 on a database with GEQO turned off.

Is this what would be expected? Does the query planner / optimizer
generally do better with explicit JOIN syntax?

Cheers,

Eric