It is definitely worth it. Dial-up internet is incredibly poor value for the speed you get. I switched from NTL dial-up to broadband about three years ago and never looked back - until we moved house to an area with no broadband and had to go back to dial-up. It was awful! Our area now has BB and I've just signed up for it.
NTL cable broadband is a good, stable technology that should give you few problems. I had an engineer out twice in three years; once when the signal levels on the line went squiffy, which he fixed out in the street without coming into the house, and another time when the modem died. He swapped it for a new one, no charge, no questions asked. Yes, NTL customer services has acquired a poor reputation but if you ever have problems and the call centre's not doing it for you, you can always come here.
Installation is relatively simple. An engineer will come to get the cables and socket in the right place; you get your modem plugged in and then you do the install on your PC yourself. You can use the CD they supply to help you, but to be honest it's worth following the instructions on this site (
here) and doing it without the CD; the CD is known to do odd things sometimes.
Security - you need to have a firewall running on your PC to prevent unauthorised access to it by other internet users. Having your machine permanently connected to the 'net does make it more vulnerable but a firewall will fix that. Windows XP and Mac OS X have one built in, but there are better alternatives out there. Zone Alarm is a good free firewall. And, by the way, Macs are indeed subject to infinietely fewer nasty viruses etc. I bought a Mac five years ago and will never buy a PC again.
Other services - I think you should forget dial-up. It's expensive, slow and unreliable. If you don't go for NTL cable broadband you could get ADSL down a BT phone line from any one of a multitude of providers I have no experience with. If you sniff around these forums you'll get an idea what people think of them though.