No issues here yet with 2 subscribed and running 11.0.
I don't use Netflix at all on TiVo HD. I don't even have an active Netflix account. Both HDMI (for sound, but I don't use it to watch most of the time due to the Yamaha receiver bug, and no, the workaround listed doesn't help) and component are connected.I had periods about a year ago with frequent hangs/reboots on my TiVo HD. I attribute most of these to Netflix and using an HDMI connection.
TiVo says they put a fix for Netflix hangs in the latest software (11.0k) and I now use component connections.
I still have a spontaneous reboot every month or two. If you've had periods of a year or more without hangs, you're doing a lot better than me. Even my trusty old S2DT would spontaneously reboot 2 or 3 times a year. Other than the infrequent hangs, I see no symptoms to suggest a hard drive problem.
A hard drive starting to fail is always a prime candidate for TiVo problems. Yours is old enough for that to be a possibility.