Recently, in discussing clients for text mining applications, I've found the distinction between Google Maps and Google Earth to be a useful point of comparison.
With Google Maps, we have a think client which is little more than a script enhanced browser capable of pulling images from a server and intercepting textual and gestural input. It doesn't know anything about the geographic or physical world per se. In fact, the browser in which it is implemented is designed to understand documents, and doesn't even do that well.
With Google Earth, we have a rich client which has an intimate understanding of the geographic and physical world. It is capable of drawing pictures in 3D, of dealing with logical descriptions of cartographic features (such as borders) and has a rich form of interaction.
Using this analogy with text mining clients, we can compare browser based interactions with those provided by a rich client. The browser implemented client has some obvious attractions, such as the ability to access your application almost anywhere. However, it doesn't know anything about textual data. With a rich client, you can build capabilities into the application that enable a richer and deeper analysis. The caveat with this approach is that the data, or some portion of it, needs to be situated on the client machine. Our ability to enable this is a function of bandwidth, server response times, disc speed and CPU power - things which will always be improved.
In my opinion, the rich client path leads to a far more exciting application - compare Google Maps with Google Earth and see what I mean. By extension, I believe that the web in general is bottlenecked by the browser - a client that doesn't really understand the data that it provides interactions with (hyper text documents). There will be a time in the future when the client for the web will be unrecognizable when compared with today's browsers. The question is: are we going to get there by evolution, or will there be some innovation that allows us to leapfrog to that point?