O'Driscoll formed a superb midfield partnership with Roberts during the 2009 British and Irish Lions tour to South Africa.
However the two friends will become enemies for 80 minutes as Wales and Ireland slug it out for a place in the RWC semi-finals.
And O'Driscoll believes Roberts has become a more formidable opponent since adding variety to his game.
"Most of the Welsh squad are in good form," said O'Driscoll.
"Jamie Roberts has done well, mixing his game up well. He'll be a handful, but that's nothing new.
"Jamie carries extremely hard, but he's also brought in some nice subtleties.
"He's not afraid to mix it up and that's made him difficult to read.
"He's evolved on that front, but one aspect of his game that hasn't changed is his ability to break the gainline.
"Teams play off go-forward ball and he's one of their go-to guys for that."
Ireland will go into Saturday's showdown as marginal favourites to reach the semi-finals for the first time after going through the pool stages unbeaten - including registering a win over Australia.
One of the key ingredients behind their march through the World Cup has been their rampaging back row of Sean O'Brien, Stephen Ferris and Jamie Heaslip.
And although the trio have been touted as the best back row in the tournament, O'Driscoll insists they remain grounded despite the plaudits.
"They've been going very well. On their day they're a world-class trio and have been putting in some good performances," he said.
"But they know they have some improvements to make in their game as well.
"It's always nice getting plaudits from people outside the camp but at the same time I don't think it will affect their mindset.
"They're really enjoying along with everyone else the challenges that have been thrown at us and will want to produce it again.
"They won't let the chat about them affect their performances in any way.
"The power they bring is important, but we've had powerful ball carriers in the past.
"Maybe people have been surprised by them but we knew they've had that in their armoury for a while and it's been building.
"Ferris hasn't played an awful lot of rugby. Jamie and Sean have been playing very well for the last year."
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