I have online banking with NatWest and Cahoot and can say that I have never had any problems with either bank. I have transferred money between these accounts and paid money into other accounts without any failures.

I find it very useful that I can check my accounts at any time and perform transactions out of banking hours, and its a lot more convenient than visiting the branch and queing up to talk to somebody.

I'm not saying it would suit everbody, but I have yet to experience any hacking or whatever, and the system seems pretty secure to me.