I used to like blades......
Until I had to manage a room half full of them. Vendor lock in a described above is annoying, but not the worst trait. Wait until you have to manage firmware versions of all the chassis components, and the blades themselves. Then you discover there are firmware compatibility issues that cause a chassis to power cycle when a blade of particular version is inserted.
Or that you need to power cycle a chassis to perform an upgrade. Oh the joy of managing the contents of the chassis to do this.
I love the density and the theory of blades, but reality for those tasked with availability is not quite as rosy.
The biggest warning flag from a vendor lock in standpoint is when Cisco started selling servers. They recognise an opportunity to cup / squeeze testicles when they see it.