I rarely do searches on my Kindle 4, and when I do there's a not-as-cumbersome-as-you'd-think-but-pretty-cumbersome-anyway keyboard that you can use. In exchange, I get a smaller, lighter Kindle that's easier to pack around.
That said, the physical page-turn buttons are the best part. Without those, I'd never use the thing.
Maybe it's just me, but there are circumstances when I prefer a good index to a text search. If a term is informally introduced and used a couple of times in the few pages before it's defined, for example, I usually want the formal definition, and I can just remember that that's the second index entry rather than the first rather than Ctrl-G-ing my way through a bunch of uses.
Also, how do you search for words or phrases without a keyboard or touchpad? I find that a very handy ereader feature. Well worth $10.
Oh remember the days of paper books and indexes...