I've had similar (but not the same problem) with boot sequence today and had some interesting findings about that. First of all, syslog gives much more details than any kind of manual debug output. Then there are files in /var/lib/dsme/stats showing which startup script failed and how many times (and which one was the cause to reboot).

And finally my biggest finding - I used maemo-control-services to disable some "unnecessary" stuff like multimediad (who would need sound on N810 after all ). Afterwards I started having some problems with sound so I reenabled multimediad and decided to reboot. That's how I got into reboot loop. But fortunately I was able to boot from flash (normally I boot from external SD card), chroot into problematic partition and use syslog just to find out multimediad is dying. As I suspected, disabling it (update-rc.d is the script to do that from command line, in case anyone wonders) made the system start without problems. Moreover, I could start multimediad after bootup, but not using proper boot sequence.

I also thought that maybe /usr/sbin/multimediad file got corrupted, so I uninstalled the whole multimediad package (together with bunch of other sound-related stuff) and then reinstalled again (with the same stuff). And than I was enlightened: Maemo (like Debian, I suppose) has no boot script dependency, so disabling and reenabling services may lead to borked system. In my case original multimediad links in /etc/rc?.d dirs were prefixed by 25, while after disabling and reenabling it the prefix was 20. Considering that there is a service dsp-something with prefix 24 I guess it's quite easy to figure out why multimediad crashed after toggling it off and on again.

Btw. it really eludes me why there is no way to define boot script dependencies. I guess I'm a bit spoiled by Gentoo, which is my primary distribution for PCs, which eg. brings ssh down and up again when restarting network interface (basing on dependencies). There a situation like mine would never happen