Yesterday I upgraded from Ubuntu 7.10 to the new 8.04 RC and I "broke" my Scratchbox installation. I tried to install it again and I had still some problems logging into Scratchbox and installing the SDK.
The I found this page: http://suppressingfire.livejournal.com/35277.html
that explain how to fix these problems. In particular if you get this kind of error trying to log into Scratchbox:
Inconsistency detected by ld.so: rtld.c: 1192: dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
You can fix it in this way:
echo 0 | sudo tee /proc/sys/vm/vdso_enabled
You can read the complete fix in my updated wiki: http://www.ptlug.org/wiki/Howto_Installing_Maemo_SDK_4