Perusing your event logs, you notice a SharePoint Foundation Critical Error 3760 message:

Log Name: Application
Source: SharePoint Foundation
Event ID: 3760
Level: Critical
User: Shared Services Account
Task Category: Database

SQL Database <some_content_database> on SQL Server instance <SQL_Server> not found.  Additional error information from SQL Server is included below.  Cannot open database <some_content_database> requested by the login.  The login failed.  Login failed for user <domain\shared_services_account>.

This error occurs because the Office Web Applications and Access, Excel, Visio and PerformancePoint Service Applications require access to the content database(s) and do not have it.  When using PowerShell to deploy a farm, content database access is granted to the account running the commands/script and the service account tied to the web application.  This also appears to be the case when performing a database attach using content databases from a different portal such as a 2007 -> 2010 migration.

The fix is straightforward, although finding it was painful!  Open the SharePoint 2010 Management Shell and issue the following commands:

$wa = Get-SPWebApplication
foreach ($web in $wa) {$web.GrantAccessToProcessIdentity("DOMAIN\shared_services_account")}