I won't get too specific about the differences of PRO and Lite versions, because they can already be seen here. This time, CodeTek's VirtualDesktop comes with its own installer, but I must say I prefer the old way of just dragging the binary over to the desired folder.
The new version requires the admin password to be inserted, and I hope there is a good reason behind this. When loading the application for the first time. it will ask you for your serial number. If you want to use the app as a demo, you need to request for a free demo serial license for 15 days via the CodeTek web site.
I find a bit lame that users need to give their email addresses to CodeTek to get a demo. Granted, CodeTek only sends out emails when they have newer versions, once a month or so, but still... On to the application itself, the preference panel offers quite a few options. You can select how many virtual desktops you need and in how many rows and columns to display them in the desktop pager. If you want, the virtual desktops can only have an effect on the main display on a dual monitor setup. You can customize it to have focus follows mouse (another Unix favorite among older users), switch desktops using the mouse, to display popups during a desktop switch, and select what font to use and how opaque you want the desktop pager to be, or choose whether you want the pager to auto-hide or not. In short, there are countless options to configure the functionality or the looks and the desktop pager.
CodeTek's VirtualDesktop also supports skins. There aren't many skins yet for version 3.0, and I personally found the default be the best one available. Some users might prefer to not have a Desktop pager, but to change screens using either the keyboard (hotkey editing supported) or the VirtualDesktop entry in the menu bar. Command+Option+Right_Arrow gets you to the next virtual screen, and I found this to be a faster way of switching screens. However, using the context menu on the pager itself, you can set an application window to move to a specific screen, so the pager does have an extra usefulness. The menu bar entry lets you have access to the preference panel and to a list of all the open apps categorized under the desktop they currently live in. Version 3.0 introduces an extra step (two clicks instead of one) to get to the application you are searching for, but I guess combining the functionality of Expose in the mix minimizes the need to go to that menu too much.
An interesting feature of VirtualDesktop is the ability to have different behavior for some applications that are "special". For example, for Finder you can ask VD to switch to the desktop of Finder's topmost window when it becomes active. Or you can ask some apps to be visible at all desktops by default, or to ignore focus follows mouse and much more. VD is definitely not short of options.
For me, the best two new features were the auto-hide ability of the desktop pager, and the fact that now VD works well with all X11 window managers (previous version had real trouble with X11)! Surely, people will rush to compare VD to WSManager, an open source free virtual desktop alternative for OSX. I tried the latest version of WSManager today and it should work well for people who prefer a free ride. However, for users who need the extra functionality, VD is the best choice (plus WSManager is still alpha software). I must say, though, I am very fond of two WSManager features not found on VD:
1. Cool switching. WSManager has implemented 8 switch transitions, similar to the cool effect that Apple does when a user changes account on the fly. My favorite is the Cube effect, but "Swap Over" is also very cool. It is very nice to have such a visual feedback when changing your screen.
2. Pager to be placed on the top of the menu bar. Especially for us who run on ridiculously high resolutions with much menu bar space to spare, having the pager in the menu bar itself (4 columns in 1 row) saves real screen estate (you can never really have too much chocolate or screen space).
CodeTek's VD costs $40, but you can get the Lite version for only $20, and there are interesting upgrade options. The utility is highly recommended for power users, but also for those who are stuck at 1024x768 or less with Mac OS X. For the freeloaders, WSManager will probably do the job, but if you are after stability and features, go for VD instead. But in any case, try a virtual desktop solution in addition to Expose, they go well together.