GraphLab is intended for efficiently parallelizing Processing intensive Machine learning algorithms, this is different from "Bring Computation near data" philosophy of Hadoop/HDFS/Map-Reduce. Generally most of enterprise mapreduce application are primarily IO intensive, in that case it is important to have multiple machines accessing data from multiple disks.
GraphLab would be suitable for machines with multiple processors or the new cloud on chip machines which have ~40+ Cores.
Most of the Machine Learning algorithms tend to be processing intensive, and simple abstractions such as Map-Reduce dont help a lot, thus GraphLab has its own niche to serve.