Dec 29, 2010 11:53 GMT  ·  By

Google is always testing new features and changes and it's true for its advertising business as well. Ad units are tweaked or introduced from time to time but one ad block Google is testing in Gmail now has the potential to irritate a lot of users.

Gmail has always had advertising, but the ad placements have been rather subtle and haven't gotten too much in the way of handling the actual emails and getting work done.

But Google is now testing an ad unit that shows up under the reply box and the conversations, a lot more visible and, to some users, a lot more annoying. Ads in Gmail have traditionally been restricted to the right sidebar and to just below the header section.

While taking up a sizeable chunk of the screen real estate space, these ads are separated enough from the content that most users hardly even notice them, which is great if you're an user, not so great if you're an advertiser.

The new ads below the conversation, in an area where users regularly conduct several actions - replying, forwarding - aren't that easy to ignore. These should drive up click-through rates for Google, but a lot of users are not going to like it.

With the size of Gmail's worldwide audience, more noticeable ads should mean a decent bump in revenue for Google, but also because of the number of users, it's guaranteed that there will be complaints.

Already, in the testing phase, there have been a few who have voiced their dislike. There is no doubt that at least some users will not be pleased.

The real question is whether the number of users annoyed by the new ads is large enough to have Google worried or they can simply be ignored, which is probably one of the questions Google is trying to answer with the test.