According to twittercounter there are about 2324 Israeli twitter users, my guess is a bit higher, closer to 3,500-4,000, as opposed to over 600,000 facebook users - some even say 750,000. Twitter is still relatively un-known in Israel, and we're waiting for it to make its leap, but already I'm seeing more and more businesses entering this space, opening accounts on twitter. The reason is simple: it's easy to manage and update, and doesn't require too much of your time. The question is what value (or ROI) you expect from such activities, and the answers here vary, a lot.
a) an updated account (less than 20 days since your last twit) and
b) full bio available for contact and details.
Although the entire post is in Hebrew, by hovering over the names you can get the feeling of 'who's who' in the Israeli E2.0 arena. I'm sure the list will continue to grow (by at least 1 more) in the future.
Link:
The List: Israeli Companies on Twitter (Hebrew)