Question : I need solid benefits for using VLAN's and subnetting

I recently approached my boss with some ideas on changing the infrastructure of the company network.  The biggest changes would be adding some layer 3 cisco 3560G switches and setting up vlans across different parts of the company.  Obviously I will need to subnet out those same areas that will be using vlans.  My boss punched a few holes in my plan and therefore forced me to re-think a few things.  The main reasons I gave him for doing such a thing are as follows:

1.  Ease management of the network
2.  Increase performance by limiting broadcasts
3.  Stop virus' from propagating throughout the entire company

Could someone please look at my reasons and expound on them?  I could really use some real life situations where vlans and subnetting has saved lots of time and stress.  Specifically situations involving the reasons I listed above.

Answer : I need solid benefits for using VLAN's and subnetting

Network security and IP address allocatoin would be your best argument.

by dividing the network into vlans, you can provide security by limiting access with acls.  

setting up an excel spreadsheet with IP addresses in them can help managment also.  We have our IP addresses setup so that the first 25 addresses in each subnet are for dedicated network devices (switches, routers, firewalls), the next 30 addresses are for static IP addresses (printers, cameras, scanners, servers), and then the rest  are for DHCP.

giving each department its own subnet and the further dividing each subnet into the sheme mentioned above, you can easily tell what an IP address is used for or who is belongs to.

As for the virus,  some viruses spread through email attachments and it will not matter what your IP address is.