It seems as if I'm having hard luck with the server virtuemart.net is hosted on. The server harddisk completely crashed again (the last crash was just 4 weeks ago). As you might have found out, the dedicated server is hosted at Strato AG in Germany - this is one of the biggest hosting companies. So the downtime is not because of cheapest webhosting...but because of filesystem corruption and bad HDDs. The broken server has been replaced by a new machine of the same type.
I apologize for any troubles this downtime may have caused.
Anyway we're moving this site to a more powerful server this weekend. This may again lead to a downtime, but the site should be stable then.