Thanks to everyone who has responded. One of my biggest concerns is the add-ons, bolt-ons, extra-apps - whatever you want to call them. I had a client who connected his appointment system to Xero, and his credit card collection facility, and his bank account; the result was that Xero was counting his income three times, so he thought his business was doing really well.
Xero said it was his choice to connect them and took no responsibility at all; to my mind, this is like a doctor handing out prescriptions (all these solutions are available to you) and not worrying about any contra-indications. And as any of you will know, sorting out this kind of mess takes twice as long as simply scrapping the whole lot and knocking it out on a spreadsheet!!
The problem is we are pushing people towards doing something that they (a) don't understand, (b) are not trained on and (c) don't want to do anyway. Couple that with adverts saying how easy it is and you have a recipe for disaster.