No team can really be considered a "threat over the years" as none of them have been consistent beyond 5-6 years in a 20 year spell of United dominance. That's what makes Fergie's reign so phenomenal. Challengers have come and gone but we've always been there or there abouts, never below third since the PL was founded.
true. the best team we came up against was Mourinho's Chelsea that won the league by a daft number of points.
It was one of our poorer seasons which helped Chelseas look even better but they were machine like that season.