While OTAs are considered "voluntary," the 49ers usually have good attendance, especially when it comes to veteran players. Just look at Anquan Boldin, who skipped the Baltimore Ravens White House trip with President Obama.
Though the point is somewhat moot, considering Boldin wasn't on the practice field at the start of OTAs, according to Matt Barrows. Oh well, at least he wasn't celebrating. Not sure how that would work in the 49ers locker room.
In all honesty, the name of the game when it comes to voluntary OTAs has been injuries.
Some expected injury news (Justin Smith, Aldon Smith, Kendall Hunter, Marcus Lattimore) combined with a few head scratchers (Frank Gore, Kendall Hunter) have made OTAs a bit quieter than usual, but interesting nonetheless.
Here is an updated depth chart, post-OTAs.