I just upgraded to Piwik 1.5 (from 1.4) and decided to setup archiving via cron. I test ran archive.sh and got some errors like:
Base table or view already exists: 1050 Table 'piwik_archive_numeric_2010_11' already exists
I guess it's not fatal, but since it's reported it might be an issue. I have four sites in my Piwik installation, and Piwik is mostly used to collect data - the stats are seldom viewed.