Cash ISA's - yes,although the returns will generally struggle to keep up with inflation.
Shares ISA's - yes,as long as you treat them as long term investments and are prepared to take a little risk. The longer you keep them the more you will iron out the down turns of the stock markets.
Until recently you were only allowed �3000 to invest each year in a cash ISA. Let's see! At 6% interest earned will be �180. Big deal! Even if you had to pay tax on that is would have only bean a misely �18 for the average tax payer. Take away inflation and a trip to the BS seems hardly worth while.