The banks always advise not to do so, but as has been stated above, how else can you do transfers.
I guess one way would be to open another account (with no overdraft facility) specifically for such a purpose and by judicious filling/emptying it, keeping control on the amount available, but not entirely foolproof.
As an aside, last time I did a transfer I noticed that the banks now do a check against the name (about bloody time) which protects the long-suffering Customer from a possible typo in account number which previously quite happily swept the funds out to the wrong destination without redress.