BBC Radio 4's Home Planet did a piece on the pros and cons of Combi boilers with respect to convenience and efficiency vs stored systems.
Home Planet is billed as "A weekly programme about the environment and international development, in which informed panelists discuss listeners' concerns about the world in which we live."
The Combi piece was quite well balanced and brought up most of the points that get exercised here. Summarising, they concluded that the better combis are *possibly* ok, but the basic ones have several snags.
They have links on the Home Planet page, one of which is the "DIY Frequently Asked Questions"
You can listen to the programme online, for about a week. The combi piece starts 8 1/2 minutes in