I think a converged device is still several years away as the reader of choice for ebooks. I think this is true for several reasons.
1. If we accept that 5-6" screens are ideal for ebooks, we end up with a device that is too large to be a cell phone, but essentially too small for many of the things that people do with their PCs. Its the reason why the 7" screens that netbooks started with are rapidly being displaced by 8.9" and 10" screens. Yes you could imagine a PMP being in the 5"-6" range, but it seems like people perfer them to be more pocketable. (Otherwise you get little advantage over just having a tablet). Just a point, but UMPC's fill niche.. and they haven't exactly been a huge success.
2. Cost... ebook devices, all of them, are essentially overpriced for their capabilities. Some of this is due to the cost of eInk technology, and some is due to relatively low volumes that ebook readers sell. Ultimately though, I just can't say ebook readers are going to be willing to spend $700 for a device that they are going to use mostly for reading ebooks when I expect that in a year or two, most of these devices will probably be in the $200 range.
3. eBook readers often prefer non-backlit screens. So far at least, no device released has really been designed to be as readable in direct sun light as it is in a dimply lit room.