Hello Danny Chapman,
And Cheers!.. to you all back in the Motherland.
No, I've also have a 2005 on my G5 (wife's computer) and it was fine(and always will be fine, unless it get's knocked off and scrapes the LCD); but we went with the SightFlex for convenience of moving around the house during our family overseas chats. The fixed location magnet mount was just that, too fixed to get everyone in the picture and to see us all on holidays.
So, magnetic force and LCD are not an issue. You may be able to distort the image
temporarly with a really,really strong magnet, really, really close, but as soon as it is removed, would end the slight distortion.
Magnets and floppy's or (gasp!, tape) backup's are an issue. Magnets and HD's are possible but unlikely. Magnets and LCD's should not be an issue.
Cheers (right back at ya!),
Bill Gallagher