There are all kinds of problems with this. For one, it could just indicate that Ubuntu has more problems than other OSen and thus needs more searches. The very fact that Ubuntu has a higher number on the trend lines indicates that there are some serious problems with using this method to do the comparison.

This (http://www.netmarketshare.com/os-market-share.aspx?qprid=11) seems a more direct way to compare the shares and seem to indicate Linux is basically flat over the last couple of years. It certainly doesn't indicate any imminent opportunity that Dell might miss here. Even your trend graph shows a substantial decline in Ubuntu searches over the last year.