Hi,
I used my Kobo H2O for about 1 year and constantly have problem of freezing screen. It happen once every night after few minutes of reading, so I have to shut down the reader and to reopen it. Very unpleasant procedure for a reader of this price.
H2O seems to have more problem with epub format than it has with Kebub, but even with Kepub my reader freeze, from time to time. The problem seems also to be linked with annotations of texts (a mess on any KOBO reader). I already have a Sony PR3 for three years now and never experience such problems. I think KOBO devices are buggy and I would not recommended to anybody to buy one.
P.