The four memory channels are a big deal for those with large workloads in play, such as virtualization environments. Large enterprises are running massive virtualization environments, with hundreds of virtual machines on one physical server. The processing power isn't the issue; it's available memory, since the memory can't be shared. Each virtual machine has to be walled off for a number of obvious reasons, and that means memory allocated to each separate virtual machine.
Xeon 7500-series processors can accomodate up to 2TB in an eight-socket configuration, 1TB in a four-socket configuration, and 512GB of memory in a two-socket system, which is much more than any previous architecture. For measure, Cisco's Unified Computing System blades use two Nehalem Xeon 5500-series processors, and they needed a special ASIC designed by Cisco that makes four DIMMs appear as one to the system, allowing them to cram 384GB on a two-socket blade. Now, Intel is offering 512GB on a two-socket setup.
Memory isn't the only way the Xeon 7500-series supports virtualization. The chips contain Intel Virtualization Technologies (VT), several new hardware-based features designed to optimize the chip for a virtualization world. One of the big bottlenecks in virtualization, along with memory constraints, is I/O. When you have dozens or hundreds of virtual machines on one box all fighting for the same Ethernet port, the same PCI buses, the same memory and SATA buses, well, it can create a lot of choke points.
Intel VT includes FlexMigration, which works in live virtual machine migrations across all Intel Core and Nehalem-based platforms to allow continuous operation without interruption. It also allows processors to be added or removed from the pool of processors dedicated to virtualized systems. You might want to add a few CPUs for additional load, for instance, or free some up. FlexMigration makes it possible to add and remove them while the server is running.