As far as basic spreadsheets are concerned, Gnumeric is close to complete Office 97 compatibility, and the port loses no functionality - recent updates mostly concern code cleanup, look&feel and compatibility improvements with more recent Excel versions, and fixes for bugs you'll hardly ever encounter on any real-world sheet.

If formulas are broken, you either use a very early version, or there is something broken on setup. I've been using Gnumeric almost since it has been ported, with very formula heavy sheets, and they all work, without ever loading extra packages.

Sevo