I read a lot of ebooks on PDA since Palm, Windows Mobile, and now iPhone (got it like new at only $380 w/o contract, a bit more expensive than 6-inch e-ink reader). The beauty of them is to have ebooks with you all (almost) the time.
I never expect to read ebook in bright outdoor; but I read a lot on my bed before falling asleep, at lowest brightness setting on my phone (still too bright for me, though).
Most important for me is to read full-content news whenever I can, in train, in vet (sorry), in waiting line, etc. This could be done by retrieving those news through Mobipocket desktop and copy those prc files to my iPhone.
Another important thing is iPhone/touch support Thai language without flaw.
After researching all the ebook readers in market right now, I still cannot find one which supports both mobi/prc and Thai as good as my iPhone.
I use Kindle app on iPhone for mobi enews reading and use eReader to read ebooks (English novels, mostly) because it supports in-book dictionary lookup.
I also use Stanza to read ePub ebooks. GoodReader for pdf with reflow, DOC and Quickoffice.....how versatile my iPhone is!
I do not see battery life an issue at all when reading ebooks because I usually charge my phone every other night. This is good enough.
Having said all the above, I'm still looking for my perfect e-ink reader for in-sofa reading. My ideal ebook reader should at least support Thai and mobi format reasonably well.