currency convertor issue

...seems strange to me that MS do not offer a built-in solution for this.

I wouldn't say so... after all a cell that contains manual input can contain multiple format attributes (ie different sections could be in bold, italic, red, black etc) so it follows that performing calculations on the basis of a cells format is inherently complex.

...i'm sure there are others who face the same problem

Yes, you will find plenty of examples of this type of UDF on the web - the key is obviously not to try and differentiate between values on the basis of cell formatting
(only possible by means of formulae if there is some other underlying logic that can be aped that is determining the format itself).