Importance of dates

When browsing the web I don't want to look at old data, so when reading I try to find out when the page was last updated. Now blogging and wikis have become so popular there is normally a date associated with the post but otherwise you are normally left to guess based on version numbers of programs people used.

So if you are a web developer please never forget the date something was created.

Further I was looking for a tool which detects changes and dispays the last changed date. Google somtimes can display this but for about 80% of the pages this information is not available. Why has nobody written a tool that wgets pages and md5sums them to see it they have changed and displays this date. I know it is not always that easy, but a tool like that would be soo usefull. Maybe a firefox plugin could help.