What I like about aTakephone is that it lets me search on fields other than name (company, in particular). So I can enter "IBM" and fine all my contacts who work at IBM, which can be handy if I don't remember someone's name.
What I don't like is that I can only use T9 to search, and not the full alpha keyboard, The developer is apparently working on that.
It also integrates your favorites, call log, contact directory and dialer in one compact app, which is handy.
Takephone was one of the most powerful apps on the old Palm OS phones. If Shimon continues to develop this, as he did the Palm version, it will become a killer app.