Umpteen years later...
Useful idea to set the width at 92% of the height Nick Hebb.
It may depend on the font you have selected*: I printed out a circle from a Calibri-based sheet and got a circle where the height divided by the width = 90.2439...%
It does mean that on the spreadsheet you won't have a round circle...

* Regarding the font, see Chinchilla's #14 reply at the excelforum post "Excel will not print images at correct height/width!!").
I set the Theme font in Page Layout to a fixed width font (Corbel, although any fixed width font should do (?) ).

The best solution, I believe so far, to get actual circles in the sheet and in print preview, is to set the shape's Properties to either of the "... don't size with cells" options.