Keynote Systems’ May 2012 News & Portal Index shows LinkedIn’s mobile properties took a drop in performance after the company integrated a mobile site into their repertoire, instead of automatically redirecting to either the mobile app or web browser.

In the past year, Keynote has noticed that LinkedIn applied a great effort in developing its mobile app and now uses the same app experience for its mobile browser. While the average speed for the introduction to the splash screen is about four seconds, it takes another four seconds to get to the actual homepage, which is bringing down the speed of the site.

“Keynote best practices would suggest that they include the mobile app button on the same page as the login page to reduce the barrier to entry for the user,” says Herman Ng, Keynote mobile performance evangelist. “The more time it takes for the page to load, the faster you lose the attention from the user, regaining their interest is an uphill battle.”

Keynote references the LinkedIn case as a good example of the kind of balance that has to be maintained between aesthetics and function. While LinkedIn’s mobile site looks great, Keynote reports that the Javascript has noticeably slowed the homepage down.

“On one hand, the new mobile site looks great and feels and behaves like a mobile app, but the Javascript and CSS has slowed down the experience,” Ng said.

As the mobile attention span decreases, the homepage is a critical landing site for any mobile user. In its report, Keynotes suggests that LinkedIn may serve its users well by delaying the download of various Javascript elements until later in the user experience, after they have passed the homepage, to increase the level of engagement and interest.

Keynote reports that Twitter also sped up drastically over the past month, with an improvement of more than four seconds and a reduction in page element size by 58 kb. The homepage now just loads a single (rotating) image with the login buttons, speeding up the mobile site performance.

“Slow improvements and decreasing object count has been a key factor for their recent performance upgrade,” Ng said. “Twitter didn’t do much cosmetically, but is heeding to Keynote best practices by decreasing the size of the homepage.”