I rolled out a feature to my team, and in two days I had two reports of users being blocked by the validation of numeric input fields.  The first one figured out that somehow a space got attached to the end, possibly via cut-and-paste.  The second one, we worked on it, and there was no sign of a non-digit in the field, but we highlighted the whole field and re-typed the number, and all was well.

You may be thinking "stupid users" but these are not stupid users, these are technology folks.  Imagine users who really are "stupid."  I think, for usability purposes, the validation of numeric data entry fields should be a tad more tolerant.  At the very least, ignore or strip out whitespace characters before attempting a conversion. 

John Arrowwood
John (at) Irie (dash) Inc (dot) com
John (at) Arrowwood Photography (dot) com
John (at) Hanlons Razor (dot) com