The two most annoying bugs killed in this update are the double-tap play button and inability to call without a data connection. Now, your voicemails shouldn't automatically stop right after you hit the play button, forcing you to press it twice. Voicemails will simply play on the first tap. Also, the app no longer requires a data connection in order to make a call, unfortunately this only applies to numbers that you've called before. If it's a new number that you need to call, you'll still need a data connection.
The update also includes a warning before you compose/send a text message if you don't have a data connection. With luck, that will cut down on repeat sending of texts. And, the update also has fixes for notification delays for texts and voicemails.
Google Voice is free and available in the Android Market.