I would personally say this is a bad example of OOP usage, especially in PHP...
The primary idea behind classes and particularly *objects* is to assist in problem solving by allowing the programmer to model real world objects...
Throwing a bunch of quasi-related, but arbitrary functions inside a class...I really hope at the very minimum you are statically invoking these functions and not actually creating an object???
The problem I have with doing anything like this, is that PHP is then required to parse the entire class, which in theory could grow to rediculous sizes...as there are almost an unlimited number of fields one could potentially validate...
The other problem, is that what your really doing is basically wrapping the collection of validation functions in a namespace, which PHP doesn't yet support (to my knowledge anwyays) but using classes as an adhoc hack.
Anyways, you are free to do as you please...I personally don't like it for the reasons mentioned above...
Cheers
