I'm with Jeff. The right number of columns is the number of columns needed to support the object stored inside the database, whether normalized or in a star schema, whatever. There isn't a number that's too many.

That said, it sounds like, based on your description, that you're not dealing with a properly structured table. 180 columns to define a user and 280 columns to define a thing... That can't possibly be normalized or a fact table. It sounds like multiple functions have been jammed into a single table. In that case, it's not that there are too many columns, but that the structure is wrong. Bad structures will absolutely cause performance headaches, maintenance problems and even development and testing problems. Just overloading a column causes problems, let alone overloading a table.