For me library support, for networking in particular, has been the major hurdle. It gets problematic when too many libraries are still marked as experimental and only partially implements the specification (e.g. protocol) that they are supposed to handle. Also after a quick look at the source for some common (networking) libraries I found a few too many calls to error to feel comfortable. It's not okay for a library to bring down my application behind my back, error should be reported even if this uglifies the code and interfaces. Furthermore I think that Haskell would benefit from moving some commonly used functionality such as HTTP, SQL and XML support into the standard libraries. I haven't seen any news about the progress of HaskellNet but I guess it could solve my problems. I really don't have much problems with tool support, speed and the like. I'm convinced it's a library (and library documentation!) thing.
As for the 'popularity' of Haskell, someone made the very common sense remark that all successful languages have been promoted by some large corporation. (Please note 'successful' stands for 'spread of use', not 'quality' here.) If fp is to reach the mainstream, it will probably be because of some centralized support from outside the academic world. Maybe something like a 'Haskell Consortium' or 'Haskell Initiative' to promote Haskell should be set up. An example could be the promotion of SystemC for hardware and software co-design by the Open SystemC Initiative www.systemc.org . Availability of an IEEE standard for Haskell would also be a good thing for its acceptance, I think.
Having someone pay a group of people to hack on Haskell implementations would indeed be desirable. Without knowing the details Ubuntu looks like a promising model. If we could just find a willing billionaire out there... Cheers, Johan