I think it's more the speed, and the fact that it's not just doing the word-by-word translation, but it's doing OCR first, and, as a nice touch, it at least makes a vague effort to visually look similar to the original text (well, color at least)... and it does all this without using a network connection at all.
The 'traditional' method of firing up something like the Google Translate app, manually (and potentially painfully, if it's a language that uses symbols you aren't used to typing in on a regular basis) typing in the text, and maybe waiting for a server in the cloud to spit back response... is just crap compared to something like this. Even if Word Lens doesn't do proper grammatical and idiomatic translation (yet?), it still seems like it'd be super useful.
The 'traditional' method of firing up something like the Google Translate app, manually (and potentially painfully, if it's a language that uses symbols you aren't used to typing in on a regular basis) typing in the text, and maybe waiting for a server in the cloud to spit back response... is just crap compared to something like this. Even if Word Lens doesn't do proper grammatical and idiomatic translation (yet?), it still seems like it'd be super useful.