I had solid oak flooring put down on my my old property, initially it was glued on direct to the concrete but despite it having been kept in the house for 4 weeks before hand to acclimatise, it buckled after a month.
This meant it all had to be pulled up, re-planed, re-sanded and re-varnished after it was laid again on wooden battens with a membrane in-between.
That fixed the problem and looked great afterwards, load of hassle though with the previous method, despite using a special glue that cost �50 a tube.
I've just moved again and while I like real wood, I'm going to go with engineered wood this time which can be laid like laminate but looks just as good as real wood as that's basically what it is, albeit only a few mm sandwiched on top of soft wood.