Below is a short summary of the VMware® vSphere™ 4.0 and vSphere 4.0 Update 1 maximums as referenced from VMware's document.

Virtual Machine Maximums

Item Maximum
Compute
Virtual CPUs per virtual machine (Virtual SMP) 8
Memory
RAM per virtual machine 255GB
Virtual machine swap file size 255GB
Storage Virtual Adapters and Devices
Virtual SCSI adapters per virtual machine 4
Virtual SCSI targets per virtual SCSI adapter 15
Virtual SCSI targets per virtual machine 60
Disk size 2TB minus 512B
IDE controllers per virtual machine 1
IDE devices per virtual machine 4
Floppy controllers per virtual machine 1
Floppy devices per virtual machine 2
Networking Virtual Devices
Virtual NICs per virtual machine 10
Virtual Peripheral Ports
Parallel ports per virtual machine 3
Serial ports per virtual machine 4
VMDirectPath
VMDirectPath PCI/PCIe devices per virtual machine 2
VMDirectPath SCSI targets per virtual machine 60
Miscellaneous
Concurrent remote console connections to a virtual machine 40

Storage Maximums

Item Maximum
VMFS-General
Raw device mapping (RDM) size 2TB minus 512B
Volume size 64TB minus 16kB
Virtual machines per volume 256
Volumes per host 256
Extents per volume 32
Hosts per cluster 32
Extents size 2TB minus 512B
Max I/O size (before splits) 32MB
VMFS-2
Files per volume 256 + (64 x additional extents)
Blocksize 256MB
File size (block size=1MB) 456GB
File size (block size=8MB) 2TB
File size (block size=64MB) 27TB
File size (block size=256MB) 64TB
VMFS-3
VMFS-3 volumes configured per host 256
Files per volume ~30,720
Block size 8MB
File size (block size=1MB) 256GB minus 512B
File size (block size=2MB) 512GB minus 512B
File size (block size=4MB) 1TB minus 512B
File size (block size=8MB) 2TB minus 512B
NFS
Default NFS datastores 8
NFS datastores 64
Fibre Channel
LUNs per host 256
LUN size 2TB minus 512B
Paths to a LUN 32
Total paths on a host 1024
LUNs concurrently opened by all virtual machines 256
LUN ID 255
HBAs per host 8
HBA ports 16
Targets per HBA 256
Hardware iSCSI Initiators
LUNs per host 256
LUNs concurrently used 256
Initiator ports per host 4
Total paths on a host 1024
Paths to a LUN 8
Dynamic targets per adapter port 64
Static targets per adapter port 61
Software iSCSI Initiators
LUNs per host 256
LUNs concurrently used 256
NICs port bound with the software iSCSI stack per server 8
Targets (the sum of static targets and dynamic targets may not exceed this total) 256
Paths to a LUN 8
Total paths 1024

Compute Maximums

Item Maximum
Virtual CPUs per host 512
Virtual machines per host 320
Logical processors per host 64
Virtual CPUs per physical core 20
Virtual CPUs per physical core for vSphere 4.0 Update 1 25

Memory Maximums

Item Maximum
Size of RAM per host 1TB
Maximum RAM allocated to service console 800MB
Minimum RAM allocated to service console 300MB
Swap files 1 per virtual machine
Swap file size Same as max virtual machine RAM


Networking Maximums

Item Maximum
Physical NICs
e1000 NICs Ethernet ports (Intel PCI-x NIC) 32
e1000 NICs Ethernet ports (Intel PCI-e NIC) 32
igb 1GB Ethernet ports (Intel) 16
tg3 1GB Ethernet ports (Broadcom) 32
bnx2 1GB Ethernet ports (Broadcom) 16
forcedeth 1GB Ethernet ports (Nvidia) 2
s2io 10GB Ethernet ports (Neterion) 4
nx_nic 10GB Ethernet ports (NetXen) 4
ixgbe Oplin 10GB Ethernet ports (Intel) 4
bnx2x 10GB Ethernet ports (Broadcom) 4
Infiniband ports (refer to VMware Community Support)
PCI VMDirectPath Devices
PCI VMDirectPath devices per host 8
vNetwork Standard Switch
Total virtual network switch ports per host (vDS and vSS ports) 4096
Virtual network switch ports per standard switch 4088
Port groups per standard switch 512
Standard switches per host 248
vNetwork Distributed Switch
Total virtual network switch ports per host (vDS and vSS ports) 4096
Distributed virtual network switch ports per vCenter™ 6000
Distributed port groups per vCenter 512
Distributed switches per vCenter 16
Hosts per distributed switch 64


Resource Pool and Cluster Maximums

Item Maximum
HA Cluster
Hosts per HA cluster 32
Virtual machines per host in HA cluster with 8 or fewer hosts 100
Virtual machines per host in HA cluster with 8 or fewer hosts for vSphere 4.0 Update 1 160
Virtual machines per host in HA cluster with 9 or more hosts 40
Failover hosts per cluster 4
Failover as percentage of cluster 50%
DRS Cluster
Hosts per DRS cluster 32
Virtual machines per DRS cluster 1280
Virtual machines per host in DRS cluster 256
Resource Pool
Resource pools per host 4096
Children per resource pool 1024
Tree depth per resource pool 12
Tree depth per resource pool in a DRS cluster 10
Resource pools per cluster 512


vCenter Server Maximums

Item Maximum
vCenter Server Scalability
Hosts (32-bit OS server) 200
Powered-on virtual machines (32-bit OS server) 2000
Registered virtual machines (32-bit OS server) 3000
Hosts (64-bit OS server) 300
Powered-on virtual machines (64-bit OS server) 3000
Registered virtual machines (64-bit OS server) 4500
Linked vCenter Server systems 10
Hosts in Linked-mode environment 1000
Powered-on virtual machines in Linked-mode environment 10000
Registered virtual machines in Linked-mode environment 15000
Concurrent vSphere client connections (32-bit OS server) 15
Concurrent vSphere client connections (64-bit OS server) 30
Hosts per data center 100