said by Thinkdiff:
At the actual partition level, there's the usual EFI partition on both disks, then the CoreStorage partition that's used to create the Fusion disk, followed by an Apple_Boot partition. On the HD, this seems to act as the Restore partition for Mountain Lion.
If you boot to Lion, you'll only see a single Boot OS X partition mounted (I can't remember if it was the SSD or HD one). All of your data will be hidden.
I only tested speeds briefly, but they were noticeably worse than the SSD alone. ~130MB write vs ~250 and ~350MB read vs ~500MB. I'm not sure if TRIM on my drive is just slow or what, so I'll try again once it's had some time to settle. My results seem to be opposite of what other reviews have shown.
One thing that I'm still looking into is if the HD will spin down on it's own when not in use. That's the biggest annoyance I had with a 2 disk setup on my MBP - the HD would spin up/down all the time unless I specifically unmounted it. So far it seems to stay spinning all the time
Those read write speeds for the fusion drive are pretty bad that is why I did not put one in my new mac mini for work. I went with the dual hard drive setup because the OCZ Vertex 4 SSD that I slap in all my Mac's perform a whole lot faster. That performance boost is worth more than one logical volume.