Think you’re one of the lucky ones who hasn’t seen a promoted tweet in your timeline yet? Well count your blessings quick, because you’ll start seeing them by the end of the year.

Promoted Tweets began appearing in search results for certain hashtags and keywords on Twitter.com in April 2010. They were then attached to Promoted Trends, so that an advertiser’s tweet would appear as the first result when someone clicked through or searched for that trend. And Twitter has been slowly rolling out Promoted Tweets in users’ regular timelines, starting with dashboards like HootSuite.

Now, it appears we’ve been given a definite timeline for Promoted Tweets to start appearing in all of our timelines, regardless of how we access Twitter.

According to Direct Marketing News, Ryan Sarver, Twitter’s Director of Platform, said that all users can expect o see tweets in their timelines by Q4 of 2011. Sarver was speaking at a session of the Adobe Omniture Summit 2011.

Sarver was quoted as saying that Twitter would be putting more emphasis on Promoted Tweets in the future:

“Promoted Tweets, to date, have been a very small portion of what we do, but it’s only because it’s been in search…[Twitter will perform] targeting to find out who you are as a user [and make sure] the right Promoted Tweets to get in front of that user.”

So, be prepared for ads – albeit targeted ones – to start appearing in your regular timeline and not just Twitter’s search in the near future.