Many online financial institutions are pushing Trusteer Rapport, in large part because many customers do not maintain adequate security on their systems, and when there is transaction fraud it is the bank, and not the customer, that normally covers the losses. So Trusteer Rapport is really for the bank's benefit. Not that TR isn't a good program. But some of what it does duplicates protection that you already have with Norton, and the rest is only useful in the event that your machine becomes infected, such as TR's ability to block applications on your PC from accessing login fields.
The main complaint against TR has been that it can slow down system performance noticeably. So the trade off is a bit of added protection that you likely won't actually need, and which mostly benefits the bank by protecting your account from possible losses that the bank would have to cover, at the expense of system performance. If you tend to get infected often or are willing to sacrifice some pep on your system for the sake of covering all the bases if your system were to be compromised, then go for it. Otherwise, if your system is adequately secure and you don't surf the web recklessly, you can probably do without TR and the extra resource usage that it would require. In my case, I looked into installing the program, but decided that it was not for me. For those who may not pay as much attention to computer security as I do, TR might be a worthwhile addition.