Well, the uptime numbers keep counting without hindrance if it gets charged, so the 13 days there basically reflects the device being stable enough to run for 13 days straight on the same session.
For the record, I had to restart the device later yesterday because some leftover daemons from mcalendar (which I had deleted) were swallowing up all my resources.

As for turning it off to get in to the device later on, I wouldn't really recommend that since the power consumed from booting is enormous. Makes sense if there are some rogue processes, but turning on Offline Mode seems to solve a few problems. It would be nice if we could access that mode it gets into when "powered off" and charging (which is only two seconds away from your Maemo desktop but with all non-essential processes not running).

22:23:23 up 21 days, 7 min, load average: 1.32, 1.05, 0.62

Last restart was when I clear my debian and make clean flash to diablo.

Darn just booted mine a week ago 'cause of a program requirement, I'll see how long I can keep it going...

Quick reply...
System Up Time on Windows XP: 61 days. How many updates have I missed, I wonder?..
N900 uptime: 4 days, would have been more if not for black spells and loose battery (I know, I should be more careful when opening the back cover) and having to insert a SIM card recently.
Best wishes.
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Per aspera ad astra...

Depends.... on most of my systems around couple of hundred days... currently I think this is tops:

juice@firefly:~$
juice@firefly:~$ uptime
20:07:51 up 784 days, 5:39, 28 users, load average: 10.45, 11.38, 12.33
juice@firefly:~$