Time is flat on the web today! If the blog post/web page you're currently reading doesn't have a date, you're stuck using design cues in the hopes of carbon dating what era it came from (flashing text, and animated jpgs?) Twitter is coming to address some component of this issue, but they still face the same problem as google, delicious, etc. How to represent time in your search results.
Here's how I see the issue of "time relevancy":
For example in the "Google Web" category, if I'm looking for advice on how to choose a DSLR Camera (the bigger format digital cameras with swapable lenses) google brings back articles from 2002 and 2003 which no longer applies to todays cameras. I could go to twitter, but I don't necessarily need advice on the camera that came out today, those are too expensive!
How do we solved this for everything in between the Way Back Machine and the Real time web? Do they all need timelines? Ones that look better than mine....