The list of fixes is also quite notable. Among them crashes related to threaded drawing. We also hope to have fixed a nasty desync bug which could occur with earlier releases related to bancrupting or autocleaned companies. A full list of changes can be found here.
Please test also this new beta extensively and help to make the 1.4.0 release the best release ever

report them to our bug tracker. If you have questions, please make use of our forums.
If your the translation into the language of your choice is lacking, now is a good time to bring it into good shape (see our web translator and the FAQ for how to apply)
Only this way you can make sure that the final 1.4.0 will have a full and complete translation. At his point I'd also like to draw your
attention to the ongoing vote for the new title game.
Enjoy,
Your OpenTTD team