Microbore is not as popular as it was once was. The advantage of micorcbore is that the small bore pipe means that a smaller volume of water is contained within a microbore installation. A smaller water volume will heat up more quickly and this results in fast response times and fuel efficiencies. I contacted Mueller Europe last year (Oxford Street, Bilston, West Midlands WW147DS) who are manufacturers of copper pipe and they sent me an excellent guide on central heating ("Heating Book")which gave comprehensive advice on designing a microbore system. Try Google and access their website. Among the advantages given for Microbore are:
Less jointing, easy pipe installation, less builder's work, lower fitting costs etc.