When Twitter announced its search-based advertising model, little more than a Google (GOOG) knockoff, the market yawned. It didn't seem like much after months and months of speculation, not to mention Twitter's promises that this was something "we would love and would be awesome."

Now, the details are out, and it could be more interesting than expected. On Twitter's blog, Biz Stone lays out "Promoted Tweets," ending the jokes such as Stephen Colbert's, "So, I assume that 'Biz' in 'Biz Stone' does not stand for 'Business Model."

Twitter's new look won't be limited to the redesigned Twitter home page. Doug Bowman, creative director at the social media company, posted a screen shot of a refreshed design for Twitter Thursday, according to SocialTimes. Of course, the whole screen isn't even shown because, as Bowman wrote in a comment, "Working on what may end up a significant redesign. Not final yet. What we can show without giving away the farm."

It looks like quite a bit is going to change, and as usual, even the smallest of updates could carry a significant revenue implication for Twitter. Here are four implications of a screen redesign for Twitter (and, more important, its investors):

The Twitter ecosystem may be changing constantly, but most of that comes on the back of individual developers and outside companies. They beat on Twitter APIs to create new products that may win them glory, recognition or cash. Over the past month, though, Twitter itself has gotten into the game, releasing or announcing a handful of new features.

A new function for "retweeting" (echoing another's tweet to your own followers), changes to how trending topics are managed, and the ability to create lists are new tools intended to engage users ... on the Twitter.com website. Considered within the context of Twitter's changed terms of service this year, the upgrades may be part of a broader ad-based revenue plan.