It's pretty much what I mean when calling Haskell hard to learn. For me it's also been a steep learning curve, and my experience hasn't been altogether different than yours.

I started out maybe 5 years ago following tutorials, reading up on all the metaphors about Monads and doing project Euler problems.

After a while I started to tackle some small web related things with Haskell and had exactly your experience of running into a lack of understanding of how the system works and wrapping my head around functional datatypes.

I pretty much gave up on Haskell as a practical language at that point, but something kept me coming back once in a while.

Then at a point I had a use for making a small web service fast and the Node prototype I made performed badly and crashed in spectacular ways under high loads. I found Snap and made a quick prototype in Haskell. At that point the experience of years of small experiments must finally have made something click. In a very short time I had a very fast service using almost no memory. It's deployed in production (as a part of http://www.webpop.com) and has been extremely stable.

By now I think I've crossed some kind of barrier, and feel like I'm both being productive and having fun when writing Haskell, but it really didn't come easy to me and all else being equal my experience tells me that a good deal of my colleagues would have an even harder time.