NAS in general are great in heterogeneous file sharing environments. I would suggest NetApps as the leader in this field. In truth, a NAS resembles more of a thin client server with a specific protocol for file sharing. However, it is typically encumbered with network/bandwidth subordination and takes a processor hit. NetApps is easy to configure and administer but performance is OK.
SANs on the other hand are conducive to environments that require constant block level hits. By virtue of this, SANs access its own respective network (typically Fibrechannel) and requires no to limited admin access to your network. SANs/EMC systems are great in high transactive, high "write" type database environments. They tend to be a lot more complex and a lot more expensive but are more reliable and have significantly higher levels of performance.
In short, it really depends on the application(s) that are being utilized to weigh in between the two. I would suggest O'Reilley's SAN and NAS as a starting point. Out of all the literature I had to suffer through, it is the most concise, well articulated and seemingly unbiased book I have read on the topic.
