ESXi 5 installs & run flawlessly on my iMac:
Prozessortyp: Intel Core i7
Prozessorgeschwindigkeit: 2,8 GHz
Anzahl der Prozessoren: 1
Gesamtzahl der Kerne: 4
L2-Cache (pro Kern): 256 KB
L3-Cache: 8 MB
Speicher: 4 GB
Geschwindigkeit für Prozessorverbindungstyp: 4.8 GT/s
SMC-Version (System): 1.54f36
I installed ESXi 5 on an USB Key (SuperTalent USB 3.0 Express Duo 16GB - needs just 25 seconds to fully boot ESXi!) and put the datastores on an NFS NAS. With Update Manager I installed all current patches, so it's build 515841.
I didn't try to install on the builtin SATA disk, because that would destroy my OsX and Win7, but I'm pretty sure it would work also: the installer gave me the choice between the USB key and the 1TB SATA drive and "Add Storage" in the vSphere Client shows the "Local ATA Disk" also.
In one VM I installed OsX Server 10.6 from ISO image and was able to upgrade to 10.6.8 without any problems. No tricks were necessary. It runs as good as if it was installed directly on the machine (extept that our 15k SAS NAS is a bit faster and larger than the SATA disk of the iMac).