if the difference is speding 1200 bucks on a great steel frame or the same price on an average titanium, you'd be insane to get the titanium. But, if you have the cash to get a good titanium frame, then I'd say 'go for it'.

The weight difference between steel and Ti is about .25 of a lb, rust is a non issue, and both will outlast any Aluminium or carbon bike out there.
What you get for your extra dollars buying Ti, is a slight decrease in weight, corrosion resistance, and a ride that is a little less springy or lively than steel.

Whether its worth the cost is a personal preference. One thing for sure though - ti still retains it's mystique, it's still a pain to machine, the raw tubes cost a packet, and it welds up like a dream ( assuming you follow the rules ).