I have scratchbox running on 64-bit Ubuntu (10.10) and have done installs on various 64bit ubuntu for the last 18 months all end up working just great.

The installation guide ( http://wiki.maemo.org/Documentation/...K_Installation ) may be slightly out of date as there a few minor differences:

needing to set vdso32=0 as a boot line instead of the quoted sysctl entry

If you have a problem with missing terminals in Scratchbox (switching targets etc) see:
http://www.terabyteunlimited.com/kb/article.php?id=454