On my server? I have 3 SAS cards. Two of them are passed through to a VM along with a USB bridge so that it can see it's license key and run it's NAS software just as if it was on a standalone machine. That software is unRAID and it works well for mass storage that need not be fast and saves power by sleeping drives when not in use. Been using it for years on standalone hardware with a cat and dog collection of drives totaling about 30TB..
The 3rd SAS card is passed through to another VM running FreeNAS. FreeNAS is higher performance and can do iSCSI, ZFS, and other things. Currently I have a few drives hooked to it providing an NFS mount to the ESXi software for VM storage. It's also SMB shared for easy access.
The system boots from a USB stick into ESXi and a small SSD provides storage for the PLOP boot disk for unRAID (long story) and for FreeNAS. I also store some ISO on it for easy access. I may setup some additional storage to play with iSCSI on something I can afford to wipe and may do some ZFS on FreeNAS or OpenSolaris sometime soon - still deciding. Currently the ESXi server runs multipe Linux, Turn-key Linux, and one Win7 VM. I've gotten OSX to boot on it but the mods made the whole thing quirky and I gave up on that one.
Hardware passthru is normally used for things like USB, RAID cards, weird peripherals via ports etc. but some do use video cards for some reason like say a VM for password cracking. I think some people load multiple cards for central video distribution too via various VM but I've never tried it.
Hope that helps :-)