Can't tell. It won't run on my computer.

Which is the whole point. Gmail runs on my Mac, on my Linux machines, on my OpenSolaris server (actually, it runs OpenIndiana these days) and on my tablet. It would probably run just fine on my AIX boxes if I compiled Firefox or Chromium for them. If Google abandons it (but keep the servers running) it will continue to operate on newer computers and newer browsers until Google pulls the plug.

For a few decades people accessed email on text based terminals. There's plenty of applications with more complex UIs than email...

I have other applications with more complicated UI's also relying on HTML and AJAX and they work just fine. What kind of web applications do you have that would require Silverlight or something similar?

How about an email application that handles keyboard acceleration really well? This can be done easily with Silverlight (in or out of the browser), but not so much with HTML. That's why Gmail has crummy keyboard handling. In Thunderbird, I can tab my way around the entire interface if I want to or use keyboard shortcuts.

I'm sure the Gmail team could do a bunch of hacks to fix this, but that's the problem. You have to hack-up everything to make HTML work well as an application platform.

It does look powerful, but the font rendering is dire. So the browser gets at least one plus.

Is pagination of the data (as shown in those examples) mandatory? It seems kind of annoying to have to limit the amount of data actually in the browser at one time, especially if it's done for "performance" reasons.

Pagination isn't even necessary if you load chunks of the table as needed. You can even render proportional scrollbars if you know how large the table should be.

The trirand grid that you linked to doesn't even get keyboard or mouse focus right. It doesn't even get row selection right.

If you think that's a good grid, I don't expect you to see anything remarkable about the grid I posted.

The most remarkable thing about the grid you posted is that it won't run on my computer. In fact, it won't run on any of my computers.

Looking around my office, I gather it would run on about four or five computers out of the about 50 here.

Fine. Let's compare it to any native grid that runs on your preferred OS then.

Both of those work fine here, and there are a half dozen other jQuery grids available if you want to try them out.

You've obviously never used the Telerik components. If you want to build the thing in their demo the controls are fabulous. If you want to build anything else you'll suffer more than you can imagine. I've had the misfortune to use several revisions of the Telerik for ASP.NET controls, and the Telerik for Silverlight controls. The Silverlight controls were atrocious.

It won't even run on OS X so that's a pretty big plus for HTML UI components, given that modern web UI frameworks are all pretty reliably cross-browser.

FWIW, Silverlight does run on OS X[1]. The demo link above was for WPF. The Silverlight version is here: http://demos.telerik.com/silverlight/

[1] http://www.microsoft.com/getsilverlight/Get-Started/Install/...