If you're going to install Distributed Replay Controller

I've posted about this on twitter a few times, but I thought I should put it down somewhere permanent as well. When you install RC0, and have selected the Distributed Replay Controller, you should be very careful about choosing the "Add Current User" button on the following dialog (I felt compelled to embellish with the skull and crossbones):

In the case where you're installing in a simple workstation or VM that is *not* in a domain, if you click this button (it may also happen for the Add… button), you may experience a little delay in setup, then a non-responding dialog, and then setup will crash with the following error:

For searchability:

SQL Server Setup has encountered the following error:
There was a failure to validate setting CTLRUSERS in validaton function ValidateUsers.
Error code 0x85640004.

This is because the dialog is hard-wired to use Active Directory, since DRU requires domain users (for more info see this MSDN page). And if you are really interested in the DRU feature set, you should check out a blog-series-in-the-making by Jonathan Kehayias (@SQLPoolBoy).

When you click OK, you will not pass GO, you will not collect $200, you will simply get to start setup over. Setup tries to continue, but eventually you will get the "SQL Server 2012 RC0 Setup has stopped working…" dialog, and you will be returned to the Installation Center.

I've filed a bug about this issue on Connect (#705158). So with any luck, they'll figure out this issue quickly and maybe, by the time you install the release candidate, the updated setup files will be waiting for you (since Setup now has the ability to update itself at runtime). My advice in the meantime is to install the DRU components, but do not configure user accounts using setup. Instead, configure them after the fact as explained in Modify the Controller and Client Services Accounts on MSDN.

If you're using SharePoint 2010

You will need to install SharePoint 2010 Service Pack 1 first. However you will need to re-create any PowerView reports that were generated using CTP3.
 

If you're upgrading from CTP3

Depending on the components you've selected, you may be asked at some point during setup to produce the Visual Studio 2010 DVD. The problem is that if you switch your mounted DVD from the RC0 ISO to the Visual Studio ISO, when setup resumes it will complain about various things and ultimately the engine and other important components will fail to install.

So, you'll want to mount both the Visual Studio 2010 ISO / DVD and the RC0 ISO / DVD as separate drive letters in order to prevent setup from getting confused. This may be challenging on a VM, which can typically only be exposed to a single DVD drive from the host, unless you install ISO mounting software inside the VM. I use SlySoft Virtual CloneDrive.

If you're using a burned DVD or mounted ISO

This is a very minor annoyance, but after setup if you un-mount the ISO or remove the DVD, and forget to close the Installation Center first, you won't be able to close the dialog without using Task Manager. If you try to close it you get a dialog that keeps popping up no matter which of its options you choose:

The tasks you want to kill in Task Manager are dw20.exe and LandingPage.exe. It may take several attempts to kill all of the dialogs that have been spawned. It should come as no great shock that I've complained about this one on Connect as well (#706586).
 

In general

Setup has a few new prerequisites in RC0 that weren't there in CTP3. You should make sure that you're completely current on Windows Updates, including Windows 7 Service Pack 1 or Windows Server 2008 R2 Service Pack 1. And if you have any Visual Studio 2010 components on the box already, please install Visual Studio 2010 Service Pack 1 *before* installing RC0.