WoW Web Stats is good for sheer statistical analysis, where you can get a number for your overall dps rating, how the dps/heal ratings stack up per fight, and all sort of number-crunchy good stuff. WoWPlot is much more visual. In effect, it's almost like an Excel chart, where you can see where how your dps curves throughout the raid and the fight. As the developer mentions on his web site, one potential usage is seeing who didn't make the switch to Demon Chains during Illhoof. What I liked was being able to graph my overall dps during a raid. It'll let me see the fights were I was effective, the ones I wasn't; basically just looking at the peaks and valleys.
There's a few issues I have with it, though -- and again, I'm putting the "this is an early beta disclaimer out there."
One problem I ran into was how the timelines scaled. If I zoomed in or out, the timeline wouldn't stay centered on my current view. As a result, I had a lot of "where was I again," moments as I had to scroll around getting back to Mr. Illhoof.
The biggest issue is that drilling down to see some of the information requires a lot of clicking and zooming and right-clicking. In the previous example of Illhoof, You first need to zoom into the Illhoof fight, split out the DPS out plot by destination, then select Demon Chains on the graph, and then create a new plot by source. If you want to split out individual names, you need to double click on each one of them individually.
Those two issues make getting reports on data a hassle. What I'd love to see is some sort of a pull-down system akin to WWS. If there was a header where I could create separate plots for each player with one click, that would save a lot of time. Same thing for boss fights. If I could easily select Illhoof from a pull-down to get just that fight, and then be able to quickly create sub-plots related to his fight, I could see some real value in this program.
What I like about WoWPlot is that it's pretty pictures instead of numbers. While I appreciate the raw numbers you see with WWS, it's easy to get too wrapped up in them. "Crikey, I did 770dps on that fight, I only did 768 on the bex one. WTF!?" Being able to split out the 10 people from a Karazhan raid into a nice little easy-to-read chart for each of the people would be nice. Sometimes, It's not so easy to tell from WWS from went down, but when you see on the chart where people went down, or had to go AFK (and, lets be honest here, everyone during a boss fight at some point had, at the least, a spousal moment that "can this wait 5 minutes, honey?" is still not acceptable). If you see that one minute after Eggbert croaked the party wiped, it'll make learning from mistakes easier.
I don't think WoWPlot will ever replace a tool like WWS for sheer number crunching. That said, frankly, I think WWS is just an e-peen measuring device. You can evaluate your performance, and see how you compare against the rest of the raid, sure, but I don't think it gives you an overview of how the raid as a whole played out. Especially when you're learning a new fight and the ensuing post-raid guild drama breaks out on the boards, where everyone is accusing each other of dropping the ball, the raid leader could take a snapshot of each member's performance and post it on the boards. "Bobbo, halfway through Gruul your dps dropped by half. What happened?" "Sorry, man, I had to let the dog out then so I auto-attacked my way through it." "Oh, ok, next time leave the darn dog out all raid, ok?"
Also, because it's local, it lacks the sharing capabilities of WWS. One kind person has taken it upon himself to upload the stats from most of our raids. WWS is obviously designed to do this; it's pretty much what it's there for. WoWPlot has zero export capabilities. If you want want to share data your only option is to screenshot it. I'm getting into wishful thinking here. But since this is currently a Mac-only program, it'd be nice if it integrated with the iApps, and had an Export to Flickr option.
It's got a bit of work before I think I'd use it a lot - hay, look, there's that beta disclaimer again. The biggest issues for me are really just ease-of-use. However, I think being able to visually plot out a timeline of a raid is a fantastic idea. If you're a raider who is also a fellow Kool-Aid drinker, give WoWPlot a look-see and throw some feedback the developer's way.