Hints or tips on reducing Excel 2007 file size

Hi,

Using a large file with a lot of conditional formatting and formulas, which is slowing down then file and making it very difficult to filter etc.

Firstly, is there anyway of knowing whether the conditional formatting is causing it to be slow the most, or whether is it the formulae.

Secondly, if I clear the conditional formatting the file size still remains similar (infact it increased slightly), is there a way to reduce the file size back to pre-formatting sizes.

Lastly, any hints or tips anyone has on improving Excel file size and speed would be greatly appreciated.

Thanks.