Just read "Get to the Top of Google" by David Viney, SEO expert at Microsoft and Amazon. He is of the opinion that domain name and server location are critical to the success in the targetted geographical location. It would seem to target both Ireland and UK you need two sites (Ireland with .ie and hosted in Ireland) (UK with .co.uk and hosted in UK), however each site is designated its target location with Google Webmasters to avoid confusion? Any thoughts on this strategy?