tail -f junk.log 
   |perl -MTime::HiRes=gettimeofday -E"$|++;say gettimeofday().' '.$_ while <>"
1265410130.569 Fri Feb  5 22:46:07 2010
1265410130.56927 Fri Feb  5 22:46:08 2010
1265410130.5694 Fri Feb  5 22:46:09 2010
1265410130.5695 Fri Feb  5 22:46:10 2010
1265410130.56959 Fri Feb  5 22:46:11 2010
...
1265410131.50094 Fri Feb  5 22:48:46 2010
1265410131.50917 Fri Feb  5 22:48:47 2010
1265410131.51604 Fri Feb  5 22:48:48 2010
1265410131.52273 Fri Feb  5 22:48:49 2010 * End of first buffer full
1265410294.569 Fri Feb  5 22:48:50 2010 *** Start of second buffer full 163 seconds later
1265410322.694 Fri Feb  5 22:48:51 2010
1265410322.69411 Fri Feb  5 22:48:52 2010
1265410322.69423 Fri Feb  5 22:48:53 2010
1265410322.69432 Fri Feb  5 22:48:54 2010
1265410322.6944 Fri Feb  5 22:48:55 2010
...
1265410322.97337 Fri Feb  5 22:49:39 2010
1265410322.98039 Fri Feb  5 22:49:40 2010
1265410322.98775 Fri Feb  5 22:49:41 2010
1265410427.993 Fri Feb  5 22:49:42 2010
Terminating on signal SIGINT(2)
1265410427.998 Fri Feb  5 22:49:43 2010