Then, options were added to allow administrators to specify a date/time format, and you could see output such as 4:31pm, Thursday June 29th 2010.
Later still, it was possible to output times relative to the present, so one could see dates like 3 minutes ago or Yesterday at 6:15pm.
However, these relative dates can be nasty when it comes to anything that is going to cache the page output. If a search engine slurps up the page, its cache is going to forever be wrong, as it will be locked at 3 minutes ago even when the content is weeks old. This can also be a problem for long threads. By the time you reach the bottom of a long page, the posts at the bottom could be several minutes older than when they were loaded into your browser, so their 2 minutes ago output is completely wrong.
The icing on the cake is that all date/time instances automatically update as time goes by. If reply to a thread, your message will be posted and its date and time will be noted as 'A moment ago'. Wait a little while, and it will automatically update to read '1 minute ago' and will continue until it no longer makes sense to display a relative date.
I have yet to grow tired of seeing all the dates in a thread simultaneously update all by themselves