I agree that hybrid storage is great, but it can "easily" be done in software (there's a couple of projects for Linux, like bcache, as well as ZFS, and there's an Intel driver in Windows). Then you can pick the size of the SSD and HDD at will, and optionally make a RAIDs of the HDDs and SSDs to mitigate against the increased failure probability.
When multiple drives aren't an option, in laptops, the problem with hybrids is that you lose out on the non-performance advantages of SSD: low power usage and durability. The controllers could improve on this, by shutting down the hard drive and doing more writeback caching, but current hybrids lose on these points. (my laptop has a 256GB SSD, which I find about a factor 2 too small. I can't sync my