What's the difference between "Free" and "Professional"?

You probably noticed that you have a choice of affiliate links to use to promte Traffic Travis. One of these is for a Free version and the other for v4.0 Professional.

So what's the difference? And how does it affect you?

The Free version is a fully workable software. It'll do most of what the professional version will do. Save a few key differences:

Number of projects: The free version is restricted to 5 projects.
Data caps: The free version has lower data caps on some tools.
Print and save reports: The free version doesn't support this feature.
If you want to take a soft-sell approach, then the free version is the one to link to. However with the release of v4.0 the professional version is much much more powerful. Here's a quick run-down on the improvements..

More accurate keyword research results. Plus more detailed data.
Ability to search for domain name availability for multiple keywords simultaneously. From within the software.
More detailed analysis of SEO competition. Easily see how hard it will be to rank for any keyword
Ability to compare backlinks among multiple websites at once.
At the click of a button, find sites where you can get quality links from.
New Adsense analysis tool. Lets you find overlooked traffic opportunities.
Updated Adwords analysis tools.
Brand new interface that is more user friendly and puts everything within easy reach.
How Novice users benefit from Traffic Travis:
Provides a page analysis tool which examines the important on-page SEO parts of a page and returns an SEO "score" for the page, as well as suggestions for improving the page from an SEO perspective.
Shows where your site is ranking in the search engines for your important keywords, so you can see at a glance rather than trawling through pages of search engine listings. Traffic Travis will even keep track of your previous positions so you can see whether your site is moving up or down over time.
See who is linking to you. Traffic Travis finds your backlinks and displays all sorts of interesting information about the sites that are linking to you, including the anchor text of the link. Traffic Travis then gives you some nice summaries so you can see all the important information at a glance. This is really useful for researching your competitors' sites as well... by looking at their anchor text (and the anchor text summary) you can see where they're focusing their backlink efforts.
All tools are found in the one piece of software, so it's no longer necessary to find and visit a multitude of websites to analyze a website.
What more experienced users will be able to do:
Takes the tedium out of tasks like finding search engine positions, finding backlinks, analyzing keyword density etc. Most experienced users will have found these tools available online on various websites, but Traffic Travis brings these tools and others to the desktop, which saves time hopping around.
The ability to store and analyze historical data shows you the bigger trends in a market over time. Is your competitor's site going up or down in the search rankings? Do these keywords have a high turnover of PPC advertisers, indicating that they might not be very profitable? Which words are your competitors consistently bidding on, and which ones do they drop occasionally?
Pulls a variety of statistics and pools them into the one screen so that you can see how they all interact. For instance, you might see that you have a large number of backlinks, but Traffic Travis might tell you that they're all from the same IP address (and therefore they won't give you as much benefit).
Powerful PPC research tools. When you're paying for your traffic you want to be sure that your campaigns are going to be profitable. Traffic Travis gives you an extremely comprehensive range of data to thoroughly examine a market. Using a keyword list you can see which sites are bidding on certain keywords; whether they continue to bid on these keywords over time; the movement of ads in the search engines over time; an analysis of keywords to see which words attract consistent, stable competition.
Project graphs, reports and printing: For SEO and PPC professionals using Traffic Travis to perform analysis for clients, Traffic Travis offers reports and graphs which can be printed and given to clients.
The key benefit for more experienced users is providing a one-stop-shop for search engine optimization, rather than relying on multiple tools on multiple websites. Being able to easily cross-reference information is also a very important benefit, and allows users to save a considerable amount of time when researching their market and competitors. The PPC tools are so comprehensive and useful that they could easily be released as a separate product (in fact there are already products on the market retailing for up to USD$200).