Bridget Botelho at TechTarget brings up an excellent hidden gotcha in the Bring Your Own Device movement: enterprise licensing agreements! In "BYOD and mobile cloud apps lead to licensing compliance issues" she points out that some of the most common enterprise software licensing agreements (Microsoft's, in other words) require licensing any device used "for the benefit of the company" under the terms of the enterprise agreement.
This isn't particularly surprising to anyone even halfway familiar with the morass of licensing terms spewed out by major vendors; you can pretty much assume that you are required to sacrifice your first-born child and those of all your employees on the demand of any anonymous lawyer or third-party sub-contractor even remotely affiliated with Microsoft, Apple, or Oracle. According to Keith Norbie of Nexus Information Systems, a Microsoft Gold Certified Partner, this means that even if your employee purchased licensing for the device when they bought it, you are still committed to licensing it again under your enterprise agreement.
Botelho goes on to provide the conventional advice for dealing with this new vulnerability; run audits, exercise more control, implement policies, etc, etc. I can't help but feel that almost entirely misses the point of BYOD and does away with many of the advantages it can offer. If you have to exercise that degree of control, then it probably is more efficient to do so by eliminating BYOD in the first place and mandating corporate-issued devices only.
Of course, you tried that already, didn't you? Consumerization is a ride you can't get off of, and enforcement just adds costs. Half-measured approaches such as those suggested in the article don't seem much of a solution.
What is the solution? Go all in; avoid archaic and arcane licensing restrictions from old-school vendors by switching to alternate products. Gmail doesn't care what device you, or any of your employees, are using to access it. Or, as the article also suggests, move primarily to virtualization for provisioning apps with restrictive CALs.
The pushback on this is likely to be that key features are missing from the alternatives or that those other vendors have their own difficulties and ulterior motives to bring to the table. That may be true, but from the larger perspective there are two major factors to consider. One, do you want to saddle your operation's horses to legacy on-premises software vendors when it is becoming increasingly clear that utility computing is the future? Two, without some sort of market pressures from good consumers such as yourself, do you imagine that licensing terms are going to change favorably for you?
As with most decisions, you have to pick your poison here, and dealing with the teething problems of BYOD and utility computing services seems to me to be the more forward looking position. Taking a view of other legacy industries that have been outmoded by other vast changes in technology, it seems likely that all you will see from the Microsofts and Oracles of the world here will be increasingly desperate and grasping terms as they turn to their massive legal horsepower to drag them out of the pit of declining market share. The article points to exactly this factor, noting that Microsoft has not yet begun enforcement of these provisions, but is likely to as PC sales in general drop.