Here are several things which can currently be done in SimpleViewer-Pro but cannot be done in Juicebox-Pro.
However, new features are planned for Juicebox-Pro and will be introduced in future versions.

(1) Define a thumbnail grid using a specified number of rows and columns
(2) Position all gallery elements using a Fixed Layout
(3) Set a Background Image without using HTML/CSS
(4) Embed the gallery in a container Flash movie
(5) Change images and captions on hovering without clicking
(6) Change thumbnail and main image frame styles without using CSS

Currently with Juicebox-Pro, you can have a single row of thumbnails at the top or bottom of the gallery.
Greater control over the thumbnail layout (left and right positioning in grid formation) is on the roadmap.

There is no set time-frame for releases and no release dates scheduled for future versions.
However, you can be notified of new releases by joining our mailing list and following us on Twitter (@juiceboxgallery).
Please scroll down to the bottom of the Juicebox home page for details.

Only one new feature was added to the latest version of Juicebox-Pro (v1.1.1), namely the ability to set a background image using JuiceboxBuilder-Pro without the need to modify any code, #3 from the list above.
Please see the Juicebox Version History for details.

The next version of Juicebox is likely to introduce many more new features and fix several bugs but as it has not been finalized yet, I would hesitate to say with any certainty what features may or may not make it into the next version (and I also do not know when it will be released). However, we are working on incorporating features #1, #5 and #6 from the list above.