This seems like a very smart move for both parties and is going to massively disruptive effect on the industry. It'll be interesting to see how Google and Microsoft react (especially since Microsoft seems to be finally dragging itself out of the Ballmer dark age).

It's a perfect synergy[1], with IBM having dropped hardware some time ago and subsequently, most software, in favour of open-source + prestige R&D + consultancy services. Apple on the other hand, makes some of the best hardware around and turns a good profit doing it, and they also have some of the best software UX (if not necessarily the most powerful solutions). Put the two together and it's an extremely potent combination, as long as they can pull off the collaboration effectively. Apple is already making fairly serious inroads into corporate IT since BYOD became a thing. To a lesser extent, they've been a business brand longer than they've been perceived as purely consumer-oriented, with the design industry being the only thing that kept them alive in the 90s pre-iPod-turnaround.

It will also be interesting to see what impact this has on open source, because that's something that IBM currently supports heavily so they can avoid the cost of developing a lot of common business software in-house. This partnership might herald a preference for, for example, Apple servers running OSX, over Linux.

A more positive outcome is that we're likely to see significant improvements in Apple software to meet needs that IBM clients will demand: stuff that tends to sit on a dusty shelf for years, like fixing SMB support in OSX, might start seeing some serious engineering investment by Apple.

We also might see an end to Apple's "no rollbacks" policy, which IMO is a serious barrier to adoption in corporate environments (and is a huge pain for testing). No IT department worth its salt will ever push out a possibly breaking change like an OS update without a rollback plan, but Apple actively prevents that right now. Either that, or Apple will need to up it's release cycles to match the way SaaS is typically managed and take bug reports more seriously, although probably only when they come through a priority channel reserved for corporate customers, much like how Microsoft handles "unofficial" hotfixes that don't go into Windows update.

[1] Apologies for using the word "synergy" but it really is appropriate here.