It would be rather harsh to call ChessBase Online 1.1 (ChessBase GmbH, $4.95 in the iTunes Store) a bad application, because, strictly speaking, it achieves its modest and useful goal.
I can enter a position that I reached in a recent game...
..and discover the most popular replies and their performance...
...and load individual games to learn how top players handled the line.
Select one of the above games, and it loads painlessly. So far, so good. (Very handy for the bathroom stall at the Chicago Open, the cynic thinks.)
But on the iPhone 4, the chess board interface is so buggy and annoying (compare the interfaces for iPhone engines such as tChess Pro, Shredder, and Stockfish, all of which are excellent), that I really can't recommend this app.
Perhaps this works better on the iPad (I don't own one), but if I'm at home, I'm going to be looking at ChessBase on a laptop with Rybka running. That's not yet an option on the iPad..
The concept is great, and I love ChessBase products in general. But not this one: hold out for Version 2.0.