Editor’s note: Keynote Systems’ Startup Shootout Index provides some insight into the three-screen challenge — desktop, smartphone, and tablet — now facing anyone with a web presence. We’ll be bringing you a fresh set of data from Keynote every month. Check out previous Startup Shootout results.

The “three screen challenge” is a very real challenge for startups. We’re seeing numbers from industry researchers like IDC and Gartner saying the sales of tablets and smartphones have finally eclipsed desktops and leaders such as Facebook and Yahoo! are putting a major focus on mobile development.

One area we see where progress can be made is in addressing the current lack of focus on tablets. Today, most sites are delivering the exact same website on the tablet that they deliver for the desktop experience. With reasonably generous screen sizes, compared to the challenge of smaller smartphone screens, many sites choose to develop a single look-and-feel for the desktop and tablet environments.  What we know is that few companies want to have a separate desktop-optimized site and tablet-optimized site.  A site may look great on a 10” or 11” tablet, but is that the only criterion for success?

We know that looking at a desktop-sized web page on a smartphone is painful not just because of the smaller screen, but also because mobile 3G network connections are slow and media-rich, large format pages take a long time to load.  Many tablets are also used on slower mobile network connections or on congested public WiFi hot spots.  When we measure the performance of startup sites using a tablet device profile – in our case an Apple iPad – it’s working over a real 3G mobile network. And performance is often quite poor.  What we see – and what Keynote recommends – is to optimize more with the performance of 3G mobile networks in mind.

What may have minimal impact on a desktop site can make big improvements for the tablet user experience. The most important factor to keep in mind is that you’re dealing with a much higher latency when using a 3G mobile network. Every single round-trip conversation between the web browser and the web server sees this extra network delay. Any opportunity to reduce the number of round trips is a plus for performance. This includes avoiding unnecessary redirect, consolidating external CSS files to just one file, consolidating Javascript file, and using CSS sprites or data URLs wherever possible. Having one to two JavaScript files versus the seven to eight more common to desktop sites is a best practice for performance. Optimizing for a tablet site means keeping the number of HTTP requests as low as possible.

For more on the importance of optimizing for mobile,  check out the “Commerce: Mobile experience determines whether you live or die” track at VentureBeat’s MobileBeat conference, July 9-10.

Glu comes Un-Glued

We made an interesting observation this month about Glu, the freemium mobile gaming company. In the past, when site visitors arrive using a smartphone like the Apple iPhone 5, they have received a version of the site home page that was optimized for mobile. This makes sense, as it’s a mobile gaming site. For example, it offers login up top, where it’s easy to see.

But on the afternoon of June 18, the site no longer offered the mobile version of the site to its smartphone users.  Smartphone users now get the same desktop-optimized version of the site. Very strange. Before the change, the Glu mobile site home page was loading in the range of seven to nine seconds. After the change, it took 18-20 seconds to load the desktop version of the home page. A 30 element page load went to a staggering 65 elements, and the site went from 280 bytes to 965 Kbytes. That’s got to hurt. It doubled the number of HTTP requests.

We don’t know why Glu would make this change but it demonstrates precisely the difference between and desktop and mobile-optimized site.

In the quest for optimized sites, we know the pitfalls but also some good methods for making the most of what (resources) you have. These techniques for optimizing the tablet experience actually work well for the desktop too. So – if you have to make some tough choices, focus on the tablet and that will take care of the desktop experience too.

To view the full range of Keynote Indices, please visit here.

Keynote tests the sites in the index hourly and around the clock from four locations over the three largest U.S. wireless networks, simulating visitors using three different devices. Data is collected from multiple locations and then aggregated to provide an overall monthly average in terms of both performance and availability.

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