WIFI or 3g? How secure is your WIFI connection? Would you use your lap for online backing? Would you use your 3g phone for online banking? If you answered yes then go for it. In you answered no then off to the bank you go.
Yes, its as secure if not more secure that using your computer/laptop. I wouldnt however use either the ipad or a laptop on an unknown wifi hotspot like the free hotspots at a coffe shop or the airport. Someone could be monitoring those.
Yes, I would use online bill pay. I downloaded an app from the Appstore from my bank and I am pretty confident that I can pay all my bills securely. I do not see any difference between my Ipad over secure wiFi and a laptop over the same network.
I definitely do my banking on my iPad - even online bill pay on both secured and unsecured wifi networks. It's the same internet whether you're on an iPad of laptop, but the difference is that there are no key logging programs that can run in the background on the iPad like on a laptop or other computer to steal your passwords or credit card numbers when you type them in. You can even do your banking on an unsecured (open) wifi network as long as the banking site you're dealing with has a secure SSL connection. It's indicated by "https://" at the beginning of the site's URL or a little padlock icon will appear at the top of the Safari window on the iPad/iPhone. Even if you're on an open network, the data you exchange between the banking site and your computer is encrypted, so no need to worry. Just make sure your know what to look for to ensure you have a secure connection.
I use my desktop all the time for on line banking. So what is the difference, is that what you are saying?