Spce reclaimation is realy a tough topic ..
Depending upon the array the space reclaimation varies, because the when you create a LUN as thin, many things you need to consider.
1- you need to check if you have enterprise license, then only you get the VAAI features
2- you array is VAAI capable
With the latest vsphere5.0 update2 and 5.1, the esxi UNMAP issue is solved
So basically the reclimation happens or need to do in 3 level
1- In the Operation system level, that is using SDELETE for windows, FSTRIM for linux, but for EXT4 linux os it is inbuilt, and you can do it maually or automatically. For windows 2012 also it will happend automatically
2-In the VMFS level, you can use the vmkfstools in the latest esxi, to recaim
3- In the storage level, in the storage array also some times you need to do. Some arrays it dont need,
- Calculating total reclaimable space now consumed by snapshots - you will get this in the storage views from the vcenter
- Calculating reclaimable free space within the guest OS and Calculating reclaimable space by moving to thin provisioning with vmkfstools whitespace reclamation - i dont think any formula exists, 100 % answer is difficult
- Any space management benefits of VMFS 5 - it has, now vmfs supports the UNMAP, that is good. More over, it has other great features like 64 tb single LUN, full support for VAAI, 1 mb block size,
also check the VMFS heap size, this is important thing we need to check. refer my blog - http://pibytes.wordpress.com/2012/11/13/esxi-vmfs-heap-size-blockade-for-monster-virtual-machines-in-bladecenter-infrastructure/