As you might have noticed SharePoint 2010 has quite a few Application Pools running. Spence posted a series of blogs about SharePoint 2010 Apllications Pools.

SharePoint Server 2010 Worker Processes
More on SharePoint 2010 Application Pools
Application Pool miss configuration in SharePoint 2010

Besides that he posted a new version of te Application Pool Manager V3 a very handy tool for every SharePoint 2010 developer.

If you're running SharePoint 2010 on a Domain Controller you need to add a ACL Access Rule to enable Sandboxed Solutions. Without this Acces Rule the Microsoft SharePoint Foundation User Code Service will start but the SPUCWorkerProcess.exe won't.

Run the following PowerShell command to fix this...

$acl = Get-Acl HKLM:\System\CurrentControlSet\Control\ComputerName
$person = [System.Security.Principal.NTAccount]"Users"
$access = [System.Security.AccessControl.RegistryRights]::FullControl
$inheritance = [System.Security.AccessControl.InheritanceFlags]"ContainerInherit, ObjectInherit"
$propagation = [System.Security.AccessControl.PropagationFlags]::None
$type = [System.Security.AccessControl.AccessControlType]::Allow
$rule = New-Object System.Security.AccessControl.RegistryAccessRule($person, $access, $inheritance, $propagation, $type)
$acl.AddAccessRule($rule)
Set-Acl HKLM:\System\CurrentControlSet\Control\ComputerName $acl