People are going to face this upgrade one day. It's certainly better to face it now if you have the resources, than having a major upgrade difficulty when for example, ESXi 5.0 comes out (and ESX 5.0 doesn't) and you suddenly need the functionality.
4.1 is the last version of ESX classic.
1) So making a host profile of a esx 4 host and then wiping it and loading esxi 4.1 and applying the host configuration should work?
2) The host profile is stored in the vcenter database?
3) I assume when i eventually replace the three current hosts with new hosts, i will not be able to use the host profile from the old host and apply it to the new host? I will be moving from IBM servers to Dell.
Host profiles are independant of hardware (dell to HP).
Anything that doesn't apply simply errors. For example, if I built a host profile on a server with four NICs, and applied it to a server with two NICs, it sets up those two NICs to reflect vmnic1 and vmnic2 on the first server, then errors about the others.
In general all these things will be fine.
What I plan to do is setup the 3 new Dell servers to run along side the 3 current IBM servers then cold migrate the vms to the new Dell hosts. We have 3 Virtual Switches one for VMkernel/Service Console (do i still need service console w/ ESXi?) one for a couple of vlans our VM's run in and one for iSCSI/NFS . Each virtual switch has two nics which act as primary/failover. Where i get confused about is how do i know what vmware will identify as vmnic0,1,2,3,4,5 on the new Dells compared to what is setup on the IBM's already? If i could connect the 6 nics to the correctly configured ports on our switch i should be able to apply the host profile as you mentioned exactly.