Old domains registered before 2000 have much higher trust PR like domain with 2 years age and also usually in them interested seo trades.
Dailly aprox 50-100 domains expiring which been registered under 2000 year.
Usually are indexed in major search engines, sometimes also listed in DMOZ, Yahoo directory and Google directory.
Expired domains are also much better for search engine optimalization, make this process much easier, because have trust and age history.
Over 10 domains with pr5, over 30 with pr4 and hundreds with pr1 to pr3.