What I would like to invalidate are individual cells.  And I don't want to
only know about a bounding rectangle.  There is a bunch of work that
potentially has to get done to draw each grid cell.  Rules may have to run.  
Formatting has to take place, etc.  So I only want to draw the cells that
need to be drawn.  As in the example I gave, if only the upper left cell and
lower right cell need to be drawn (lets say their underlying data has
changed) I don't want to get a bounding rectangle since that would cause me
to redraw all cells.  With the bounding rectangle I realize that at some
point when I attempt to actually render to the screen that most of the
drawing would be clipped, but I've already done most of the work by this
point which in this example would have been wasted as only two cells needed
to be updated.

I'm still reading up on a bunch of painting docs so maybe things will become
more clear soon.  I've dumped some information in my sample application and
it doesn't make sense to me.  I created a user control while I dock fill to
my form.  I override OnPaint() in this user control and dump out the clip
rectangle from the PaintEventArgs and the clip bounds from the graphics
object.  This is what I get:

clip rectangle: {X=0,Y=0,Width=0,Height=0}
bounds: {X=-4194304,Y=-4194303,Width=8388608,Height=8388608}

I get the same values each time I size the window.  The clip rectangle is
empty.  What does this mean?  That no drawing needs to take place?  If so,
why did I get a WM_PAINT message?  And why would I get an empty clip
rectangle when I resize (larger) the window?  And why this huge clip bounds
that is rooted at some negative origin?  Is this just uninitialized data
since the clip rectangle is empty?