class MyCommentForm(CommentForm):    
    __metaclass__ = CommentMetaclass
    name = forms.CharField(initial='Name', label = '', max_length=50, help_text='Today date in text input.')
    comment = forms.CharField(initial='Text',label ='', widget=forms.Textarea)
    
    def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if comment != 'Text':
            if num_words > 2:True       
        else:        
            raise forms.ValidationError(u'Введите Ваш Текст')
        return comment  

 И так:

def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if comment == 'Text' or num_words > 2:       
            raise forms.ValidationError(u'Введите Ваш Текст')
        return comment

    def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if comment != 'Text' and num_words > 2:
            pass
        else:        
            raise forms.ValidationError(u'Введите Ваш Текст')
        return comment 
# или так:
    def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if comment == 'Text' or num_words < 2:       
            raise forms.ValidationError(u'Введите Ваш Текст')
        return comment

 if comment != 'Text':
            if num_words > 2:True  # "Это я уже от без  исходности начал тупить!
****
        if comment == 'Text' or num_words > 2:  # А тут знак сравнения, кажись не в ту сторону
            raise forms.ValidationError(u'Введите Ваш Текст')

>>> # Упростим
>>> def clean_comment(comment):
...         num_words = len(comment.split())                      
...         if comment != 'Text' and num_words > 2:
...             pass
...         else:        
...             raise Exception('Введите Ваш Текст')
...         return comment
>>> clean_comment('Text')
Traceback (most recent call last):
  File "<pyshell#10>", line 1, in <module>
    clean_comment('Text')
  File "<pyshell#9>", line 6, in clean_comment
    raise Exception('Введите Ваш Текст')
Exception: Введите Ваш Текст
>>> # OK
>>> clean_comment('Text text text')
2: 'Text text text'
>>> # OK
>>> clean_comment('buzz')
Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    clean_comment('buzz')
  File "<pyshell#9>", line 6, in clean_comment
    raise Exception('Введите Ваш Текст')
Exception: Введите Ваш Текст
>>> # OK

>>> class F(Form):    
...     name = forms.CharField(initial='Name', label = '', max_length=50, help_text='Today date in text input.')
...     comment = forms.CharField(initial='Text',label ='', widget=forms.Textarea)
...     
...     def clean_comment(self):
...         comment = self.cleaned_data['comment']
...         num_words = len(comment.split())                      
...         if comment == 'Text' or num_words < 2:
...             raise forms.ValidationError(u'Введите Ваш Текст')
...         return comment
>>> f = F({'name': 'Booo', 'comment': 'Burururur'})
>>> f.is_valid()
16: False
>>> for k in f.errors:
...     print f.errors[k]
<ul class="errorlist"><li>Введите Ваш Текст</li></ul>
>>> f = F({'name': 'Booo', 'comment': 'Text'})
>>> f.is_valid()
17: False
>>> f = F({'name': 'Booo', 'comment': 'Burururur bumbum'})
>>> f.is_valid()
18: True

class CommentMetaclass(DeclarativeFieldsMetaclass):
    def __init__(cls, cls_name, cls_bases, dict):
        del dict['base_fields']['email']
        del dict['base_fields']['url']        
        super(CommentMetaclass, cls).__init__(cls_name, cls_bases, dict)
class MyCommentForm(CommentForm):    
    __metaclass__ = CommentMetaclass
    name = forms.CharField(initial='Name', label = '', max_length=50)
    comment = forms.CharField(initial='Text',label ='', widget=forms.Textarea)
    
    def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if comment == 'Text' or num_words < 2:       
            raise forms.ValidationError(u'Введите Ваш Текст')
        return comment
*****************
>>> f = MyCommentForm(v, {'name':'Guido', 'comment':'Test text Ok'}) # v - что-бы не ругалось на отсутствие target_object
>>> f.errors
8: {'content_type': [u'This field is required.'],
 'object_pk': [u'This field is required.'],
 'security_hash': [u'This field is required.'],
 'timestamp': [u'This field is required.']}
# ошибки по полю comment нет.

def clean_comment(self):
        comment = self.cleaned_data['comment']
        num_words = len(comment.split())                      
        if num_words < 2: 
            raise forms.ValidationError('проверка')
        return comment