I have the 20090508 beta firmware installed. When the battery gets below about 60% & I don't do anything for an hour or so, it appears to go to sleep, i.e. only the power button seems to be active. The power button reboots. This means that my clock setting, my place in the book I'm reading, and any tags and bookmarks are lost. Is this the normal mode for this version? Is there another way to wake the reader up?

It doesn't seem to happen when the battery is nearly full.

Don't think so.
I'm currently at 51% with no problem--just picked from an overnight pause. I've gone at least as low as 31% with no problem, probably lower...
Could be a function of the reader/viewer app; I use fbreader and coolreader only.
No pdfs allowed on my bebook. :-)

I have the 20090508 beta firmware installed. When the battery gets below about 60% & I don't do anything for an hour or so, it appears to go to sleep, i.e. only the power button seems to be active. The power button reboots. This means that my clock setting, my place in the book I'm reading, and any tags and bookmarks are lost. Is this the normal mode for this version? Is there another way to wake the reader up?

It doesn't seem to happen when the battery is nearly full.

It could possibly be a problem with the battery controller inside your battery?
A normal orderly power down does not loose the place in the book that you are reading, so you must have had a power problem that did an abrupt power down?

I've seen this myself though rarely. I'm seriously considering getting an original Nokia battery.

And the place in the book tends to be preserved in most cases for me.