The closer I look at how a manager does their thing, the more it stays the same.
In the end, a manager is just someone doing the work--work the band doesn't want to do themselves or that they can't do themsleves. And it's not parasitic: it's a managers job to make the band more money and make their life easier, and they're incentivised because they take a percentage of all the money a band makes no matter where it comes from, including of course sales from digital downloads and streams and Internet radio, etc. So:
--managers network to help get bands on tour
--managers try to get the band a publishing deal
--managers try to get the band a merchanidise deal
--managers try to get a band a booking agent
None of that's going to change because of the Internet (though the HOW of it will and has changed drastically).
Managers LIKE to have a band signed to a major label, of course, as the band gets an advance and the manager takes a chunk of the advance--money in hand, up front. That's why managers aren't as fond of indie labels, as advances are smaller or don't happen at all.
Once a band is signed, the manager "manages" the record label: they call the label to make sure all the different deprtments at the label are doing what they are supposed to do. A manager will fights for the band (labels, even small ones, have more than one project active at a time). A good manager is always at the label, trying to raise money for marketing spend, negotiating with the label for contracts, etc. If the Internet and the distributed services it offers means no contracts and/or no label at all, then I'd say a manager's job is to shepherd the band so it gets all the things a label would provide, such as digital distribution at TuneCore (my personal favorite).
One thing about the manager is never going to change: the manager is a "parent" to the band and helps them all get along, deals with crisis, and most of the time hits up friends, family and their own mortgage for money.
If the role of the manager is going to change, it'll be in how they conceive of making money using the Internet, from endotsement deals and from working with corporations to help bring in money in new ways, as well as build a solid, working knowledge of how to market the band on-line
What will impact the manager role most? Advances. Managers MUST get over making their money on the advance: if they dont, all they will do is try to get the band "signed" so they can get their pay day--the mark of a bad manager, or at least one who doesn't care much about the band or the music.
The best managers are ones that start with the right question: where does the band want to go? What is "success" to them? That should come first, because it sets the reasons why a band should want to have that manager in the first place:
1) The manager can help them acheive things they can not own thier own
2) The manager can make them more money so even after they take their cut, the band is still doing better than if they do it on their own.
The truly GREAT managers don't just do these things, they educate the band members so they know how the music world works, the value of their rights, how publishing works, performance royalties, master-use licensing and on and on. As managers take on duties they would have pushed to the labels in the old days, such as directly marketing the band, the manager who really cares will consider the artists partners and work with them.
Heck, for every old-school manager with a rolodex and a proven track record, there's "these kids today" with their computers and "inter-nets" who could probably teach the manager a thing or two about how fans get to know and experience music!