> I see that httrack uses if-modified-since attribute
> to check if the file is modified or not. But for
> dynamic pages (aspx) this attribute will always
> return the date time when the page is requested. 
> This way httrack ends up updating the complete site
> even if only one or two pages are updated. 

<http://www.httrack.com/html/faq.html#Q3b>