The OS suggestion seems unlikely - the bug only started happening in the last few weeks and I've been upgrading to the latest MC pretty much weekly for months and months (with no OS change).
All of my music is WMA Lossless. It's all stored on a network drive (relative to the machines running MC), "\\Core\Music". I rip .WAV files with EAC, put them in the right directory, import them into MC, fix up their tags, and then every so often have MC convert them to WMA lossless. They're are currently no WAV files in there. There's a largish amount of music (11,500 files, 240 gb).
One thing that strikes me as suspicious is that I just set things up such that my actual library (not just the music) is on that network share as well. (Each of the MC machines does have its own library, I thought pointing them both at the same one sounded a little too reckless, although it'd be nice...)
I actually have (or at least think I can get) a minidump of MC in the hung state.
I don't use any visualizations. I've installed and used the iPOD plug-in on one of the two machines, but the other is a completely vanilla install.
My system info (machine #1) is ...
Media Center Registered 9.1.305 -- C:\Program Files\J River\Media Center\
Microsoft Windows XP Workstation 5.1 Service Pack 1 (Build 2600)
Intel Pentium 4 2513 MHz MMX / Memory: Total - 1047 MB, Free - 492 MB
Internet Explorer: 6.0.2800.1106 / ComCtl32.dll: 5.82 (xpsp1.020828-1920) / Shlwapi.dll: 6.00.2800.1276 / Shell32.dll: 6.00.2800.1233 (xpsp2.030604-1804) / wnaspi32.dll: N/A
Ripping / Drive I: Copy mode:Normal CD Type:Auto Read speed:Max
Drive J: Copy mode:Normal CD Type:Auto Read speed:Max
Drive K: Copy mode:Normal CD Type:Auto Read speed:Max
Drive L: Copy mode:Normal CD Type:Auto Read speed:Max
Drive X: Copy mode:Normal CD Type:Auto Read speed:Max
Drive Y: Copy mode:Normal CD Type:Auto Read speed:Max
Drive Z: Copy mode:Normal CD Type:Auto Read speed:Max
Digital playback: Yes / Use YADB: Yes / Get cover art: No / Calc replay gain: Yes / Copy volume: 32767
Eject after ripping: No / Play sound after ripping: No
Burning / Drive X: PLEXTOR CD-R PREMIUM Addr: 1:0:0 Speed:52 MaxSpeed:52 BurnProof:Yes
Drive Y: _NEC CD-RW NR-9100A Addr: 1:1:0 Speed:40 MaxSpeed:40 BurnProof:Yes
Drive Z: PLEXTOR CD-R PX-W4012A Addr: 3:0:0 Speed:40 MaxSpeed:40 BurnProof:Yes
Test mode: No / Eject after writing: Yes / Direct decoding: Yes / Write CD-Text: No
Use playback settings: No / Normalization: None