Take a look at the Western Conference two guards:

Utah - Brewer, Korver
SA - Mason, Ginobili, Hill
Sac- Kevin Martin
Por - Roy
PHX- J Rich
OKC - James Harden
NO - Mo Pete, Rasual Butler
Minny-  Q Richardson, Corey Brewer
Mem - Mayo
LaL - Kobe
LaC- Eric Gordon
Hou - Tmac, Ariza
GS - SJack, Magette, Morrow
Den - JR Smith, Afflalo, Sonny Weems

Outside of Kobe, Roy, and a healthy Ginobili, who on that list is so bad ass that Josh Howard can't guard them?  And we're asking Howard to guard them, not play Artest/Bowen level stoppage on them.   With LA, having Marion and Ross on Kobe, I have no problem with Howard on Artest,  you'd want Artest taking as much shots as he wants on that team anyway.  With Portland, having Marion and Q guarding Roy, I have no problems with Fernandez and Outlaw trying to carry that team.  With SA, Ginobili has been plagued by more injuries than Howard, don't assume that Howard can't recover and Ginobili who is older and whose injuries have been worse is going to be at 100%.  And as far as Richard Jefferson is concerned, he'll have his big games but he's more of a shooter than slasher now and really hasn't been a huge threat since he was playing with Kidd.  He's definitely going to enjoy those corner threes but if San Antonio is running their offense through him, I'd call that a plus for the defense.

Outside of those three, the guys who'll probably give him the most trouble are George Hill and OJ Mayo because of their quickness and point guard ability.  However, Mayo plays on a crappy team and Hill looks good but who knows how much consistent playing time he's going to get on a nightly basis. 

Somebody needs to put to bed this Howard, quick 2 guard debate.  It's ridiculous.  The elite players at the position aren't guardable  no matter who is defending them.  DWade, Kobe, every team has trouble stopping them. That's not solely a Howard or Dallas Maverick problem.   And that's why we signed Quentin Ross and Marion, for the tougher matchups and still have Kidd/Terry for the quick smaller twos.  Throughout the game Howard isn't going to be the only defender on these guys, the Mavs have a couple of guys they can throw at them.  To me the Mavs problem has never been perimeter defending, it's having Dirk's soft tail on the inside.  Teams who have played great consistent defense have always had two sturdy posts in the lane to step up on penetration.  Guarding individual superstar talent is a team effort, one guy can' t guard them.