My parents where a little concerned to find their company website had dropped of Google's search index. In fact the mirror copy on this server (which curiously isn't linked to from anywhere) turned up higher in the search index. In fact searching using the site: keyword shows no results (which compares to the 500 or so of this domain).
One reason could be the pages are a little stale. The majority of work over the last few years has been bespoke stuff or shipping existing units which hasn't mandated an update to the web pages for a while. The other thing I noticed is that a lot of the higher search hits where link farms. I know Google has various algorithms for punishing link farms but I'm not sure if that extends to the domain they link to (which would be anoying as they never asked to be added to a link farm).