BB is still, technologically, the best corporate solution. The device can be fully encrypted, for one. The integration with corporate email is also second to none.
The reason they're losing, though, is that the price differential is simply getting too large. I realize there are a lot of armchair IT folks here, myself included, but you'd be surprised when you see what it costs to deploy BES, handsets, and all of the licensing costs involved. RIM has pushed corporate to the point where they're looking at other devices, especially Exchange + Windows Phone/Windows Mobile, as "good enough" given the price point.
You do need to step back and separate the technology and its costs for the bigger picture. Corporations have deep pockets as a general rule, but the large ones don't spend stupidly. IT is a cost center at most, and every dollar spent there is a dollar that can't go toward marketing, sales, and the product.
RIM isn't dead, but they need to focus on becoming a better value. I guarantee your corporate IT decisionmakers do not care one bit whether the handheld device is the coolest, latest thing. They do care that it's secure, stable, and user-friendly, because security breaches, product downtime/replacement, and support are all major cost drivers.
