bootchart: meaning of dotted lines introduced with lucid

I'd say the dotted lines are just a graphical gimmick for users not to get bored or worried, showing them that something is going on. I rather don't think it's meant to point exactly to a single process.
BootChart actually shows the seconds when a process was issued.
http://www.bootchart.org/images/bootchart.png

Logfiles, e.g. syslog, also provide the time.

You can also delete 'quiet splash' from grub file.

@Sam: thanks for your reply, but the lines are nut just gimmick or similar to the waiting mouse cursor - the last is not needed anyway, as the chart is not being created real-time but as post-processing after all action has finished ...

After analyzing the pybootchartgui files in detail, in the meantime I found out that the first dotted red line is drawn at the start of ureadahead process, the second line at the start of the X.org process, the third at the start of the gdm-session-worker process, and the fourth represents the startup time printed in the header (i.e. when the desktop startup has finished).

Can someone explain the significance of the ureadahead and gdm-session-worker start events within the boot process?

Reference.
http://ubuntuforums.org/showthread.php?t=1434502
https://lists.ubuntu.com/archives/ubuntu-devel/2009-June/028308.html
http://upstart.ubuntu.com/

Thanks!
Problem solved.