Highlight the issues in Cluster Computing?

Some of the issues, from a user perspective:

1) The connection speed between nodes can be a bottleneck. If the connection speed is not supreme (read Mellanox like), the processing speed of the individual nodes does not matter since most of the jobs are decomposed on several connected nodes.

2) Scheduling of jobs (in case of multi-user environments) can be a pain.

3) Clusters support only certain versions of Linux (this is not such a big issue).