Have you tried capturing any of the traffic going over the wire during that time? Try sticking a protocol analyzer on it and see what you can dig up - I know it's saved me time in the past :)

Disable Antivirus

Thank you both for the comments. Pat was dead on - I turned off Norton's "Auto-protect" and, while it still generated a bit of network traffic and took a good 30-40 seconds to load, it sure beats waiting for 5 minutes. Perhaps Subversion is in my future...

Fix For Slow or Hanging Visual Studio Using CAB, SCSF and SourceSafe
Author: Jeff Noble

FOR INSTRUCTIONS ON THE MAY 2007 RELEASE CLICK HERE!!Purpose

This document explains how to fix the problem associated with CAB, Guidance Packages, Visual Studio and SourceSafe (vss).

Symptoms
There are a couple of symptoms associated with this problem. They are depicted below:

Opening a SourceSafe bound CAB solution takes excessive time.
Right Clicking folders in a CAB/VSS solution causes an extended wait and blinks the hourglass cursor continually.
Closing a CAB/VSS solution or Visual Studio when a CAB/VSS solution is loaded. Causes Visual Studio to hang with a blinking hourglass cursor.
Resolution
Open GuidanceAutomation.sln (located in Microsoft SCSF).

Open the file ViewTemplateReference.cs. You can find it in the SmartClientDevelopment project in the References folder.

Locate the ContainsReference method and comment out (or remove): vsProject.Refresh();

Build the solution

You must register the package after you build it. I chose to replace the existing package. That way it always uses my change as I consider it a bug for my purposes.

You can replace the original by copying the SmartClientDevelopment.dll to the debug directory in the SCSF Guidance package. To do this:

Copy SmartClientDevelopment.dll from “C:\Program Files\Microsoft SCSF\GuidancePkg\Source\SmartClientDevelopment\bin\Debug”
Overwrite the existing dll in “D:\Program Files\Microsoft SCSF\GuidancePkg\bin”

Old post, but works for the same problem in Visual Studio 2008. Thanks guys!