I read somewhere that the new firmware for the GH1 does not allow the use of after market batteries?
Any news about this?

Yes. You will not be able to use third party batteries with 1.2 or higher firmware.

That said the firmware hack can disable it so you can continue to use third party batteries

Nice to know.
Thanks

There are quite a few people using aftermarket batteries on the GH1 with firmware 1.2+. I bought and used this one:

New Battery for Panasonic Lumix GF1 G1 GH1 DMW-BLB1 (http://stores.ebay.com/Digi-Battery__W0QQ_sidZ236211088?_nkw=gh1&submit=Search)

Using Dave's link, and the GH13 hack, I purchased two batteries - they work great. Run times are as long as, if not longer than, the stock Panasonic battery. Well worth the purchase, and the GH13 hack is maturing very nicely (I recommend - just be smart which features you turn on).