Ask HN: Hype vs Reality? What technologies with a good press disappointed you?

I don't want to sound like a troll. But a lot of times I found myself asking how some technology doesn't have an obvious feature or trying the new hyped technology and failing miserably after reading a zillion of good blog posts.

For example:

- Messaging systems without contention management based on blocking producers, while this is an obvious part of the Queue theory.

- Embedded databases failing with massive amount of data.