Q1) Is this plugin compatible with the current versions of WordPress and NextGen Gallery?
A1): Yes – the plugin is tested with current version of WordPress and NextGen Gallery as soon as possible: See the Demo Gallery for complete details
Q2) When I turned the plugin on, it broke the gallery. The thumbnails are now in rows of single images and there are other problems.
A2: I am sorry this happened. Usually when thumbnails become rows of single thumbnails, there is a stylesheet problem. Either 1) There is a style rule in the theme that contributes to this; or, 2) There is a style rule in another plugin that adds to this problem. If you can find a way to look at the rules and see where your styles are coming from, you may find the conflict.
Q3) Can I change the lightbox to prettyPhoto?
Yes. To use prettyPhoto with ShareMyGallery: 1) Install the prettyPhoto plugin for WordPress: http://wordpress.org/extend/plugins/prettyphoto-media/
2) Then go to the NextGen Gallery > Options > Effects Change the Link Code Line to this: rel=”prettyPhoto%GALLERYNAME%”
Here is a screenshot of the results: