This line should fix the formulas - at least those supported (fpspreadsheet does not support all formulas which Excel offers), but nothing else.
The basic cell formats should be there (color, font, text justification etc). Conditional formatting is not supported, hidden columns neither. Cell protection should work,maybe you should use the trunk version, I am not sure if this is already in the current release version (and this reminds me that it's getting time to release a new version soon...).
Hidden columns should be easily implemented in principle, but might probably cause a major rewrite of the grid. No plans for conditional formatting. So, don't expect anything to happen here too soon.