Whether an eBookwise is worth it is a personal – and flaky – decision. Some people who stare at an LCD computer monitor during the day and at an LCD TV at night find staring at an LCD reading device too much, others don't see the problem. I like reading a self-lighting unit in the dark, others shudder at the thought.
On annotations, forget them. They don't really extract to computer. (I think there's a program here that extracts them, but it's just as pictures. It's definitely not text, not searchable.) Consider them as margin notes in a paper book: bound to it, in your writing, not searchable or exportable.
At $90, if the unit lasts a year, that's two bucks a week, which is less than I pay for magazines I read and recycle-bin. Even less if you're an eBay sort (something I could never be). While ETI Technologies has shown an e-ink prototype
on their site, it's been there a long time and I have no faith in them producing it, perhaps because their market is into self-lighting and good ergonomics.
There will no doubt be a half-dozen new readers in 2010, and some will likely meet your requirements, though they'll certainly cost more, maybe much more. A cheap eBookwise lets you play with the general practice of reading ebooks on a portable device, to see in non-theory what it's worth to you. As long as you're willing to do conversions yourself (if picky) or accept rough automated format switches (if not), an eBookwise is probably worth it.