Time based fragement caching

Hi Guys,

I googled and found that time based fragment caching isnt something
out of the box. No worries, I’m sure someone wrote a plugin for it.
Any pointers? Whats the preferred pattern / technique for implementing
time based frag cache expiry. I have a widget box that fetches pics
from flickr, i dont want it to fetch more than once in 10 mins or so.
Similarily I want to cache the featured profile fragment for at least
a day.

Another, newbish question, Now that memory store is the default on
cache store in Rails, this means that the cache is duplicated multiple
times in each mongrel rails right? So, if i pick up a random record
from the database and cache it, it is possible each one of my 6
mongrels would cache potentially upto 6 different records, right?

How would class attributes be handled when we have multiple mongrels
trying to update the same class attribute?

Cheers,
Aditya