Check on the stations you can receive in your area, using the postcode checker here:
http://www.getdigitalradio.com/
If there's nothing listed, that you'd like to receive, which you can't already get on FM, there's probably not much point in buying a DAB set at the moment.
However if, like me, you love classic comedy programmes, then you'd be mad not to buy a DAB set (just to get BBC Radio 7). Similarly, if you're a sports fan, a DAB set will enable you to get 5 Live Sports Extra. Or, if you're into really great music, 6 Music is well worth having. (The BBC were planning on closing the station but that decision has now been over-ruled).
Chris
PS: DAB radios don't necessarily cost a great deal of money. Mine cost me £20 in Asda.