I you don't need inter-task communications, then I agree, but the biggest problem people have with using threads is trying to use them in the same way that forks are used. This is true of whether using iThreads or pthreads, or most other forms of threading.
Frankly, my biggest problem with using threads in Perl is that the implementation isn't very good. It's slow, uses a ton of memory and has some very non-intuitive restrictions. It feels exactly like what it is - a second-rate feature added as an after-thought.