When opening a web site in Visual Studio 2008 with SQL Express 2008 on Windows 7 64-bit, it would open fine. In fact, several files would also often open fine. But when opening a particular control, VS would hang. 0% CPU usage reported, but watching the Resource Monitor showed that it was often "Waiting on Network I/O"; not always--sometimes it was reporting no problems, but the UI would never respond regardless.
Process Monitor showed that it appeared to be thrashing with something to do with SQL Server. After exploring more, we noticed the web.config that was on the development machine had a slightly incorrect connection string. It had the machine name, but not the "\SQLEXPRESS" instance name. So it should have been "MACHINENAME\SQLEXPRESS". (We never really debugged this site locally--long story--so we hadn't noticed that it wasn't correct yet. The production connection string was already correct.) As soon as we entered the correct connection string to our development database (and with a shorter timeout period this time), Visual Studio stopped hanging and thrashing trying to connect.
I'm not sure why VS couldn't detect this, why it didn't give up with an error, or even why it was trying to connect at all--that particular control didn't directly reference the database. Maybe it was trying to dereference an image URL that, if loaded on a running instance, loads the image data directly from the database? But the Casini web server wasn't launched either way, so we're not sure what's going on here. Anyway, it works now. But if anyone has any further insights, please enlighten.