* Multiple datasets
** TODO Move "type" concept to a "dataset" concept
** TODO Type information becomes annotation on dataset
* More graphics
** DONE MA plots
* Context-sensitive help
** TODO Set up a wiki with biologist input
** TODO Add tooltips with link to wiki page
* Networks
** TODO ID mapping
** TODO Layout
** TODO Linking mechanism
* Genomic visualization
* Clustering
We currently support hierarchical clustering on various distance
metrics. There are other clustering methods, but:
  * Hierarchical is easy to use (no parameters like k in k-means)
  * Hierarchical is familiar to biologists
The need to calculate a pairwise distance matrix is not a serious
restriction, because:
  * Often, the entities responding in an experiment are relatively few 
  * If above is not true, results likely too difficult to interpret
The tree plot used by exploRase is not the prettiest, but it does
provide a simple way to brush clusters. Zoom functionality might be
nice, but then it's not clear if a fine-grain view of clusters would
even be useful.
* Filtering
  * Consider methods in genefilter package.
* Lists
  * Integrate with GSEA packages.
* Misc
** DONE Test ExpressionSet support
** TODO Better formatting of numeric data (NA, sigfigs)
** TODO Set uniform user limits on variables in GGobi  
