Plotting Using PLPlot

[dsimcha]

It seems like there's substantial interest in this.  Please give me some use
cases, i.e. what would you personally use this for, and what do you foresee others
using it for, so I can start thinking about what the API should be.  I need a wide
variety of use cases because, if I design the API based only on my personal use
cases, it will end up being geared entirely toward histograms, scatter plots, and
line graphs because that's what I use regularly.

Besides use cases, here are some specific questions:
1.  Is there any need for an OO-based API, or should I just use free functions?
2.  Does anyone have any use cases where plotting is performance critical, or
should I just keep things simple/stupid in terms of the performance/simplicity
tradeoff?