Nielsen Online announced today that their research shows that 60% of Twit­ter users stop using it the fol­low­ing month. That is, Twit­ter’s “audi­ence reten­tion rate” is 40%, con­sid­er­ably less than Face­book or MySpace’s rates were at sim­i­lar stages in their life cycle.

Source: Nielsen Online

Based on his­tor­i­cal pat­terns for other social net­work­ing sites, this implies, says Nielsen, that Twit­ter’s reach will ulti­mately be lim­ited to only 10% of con­sumers online:

To be clear, a high reten­tion rate doesn’t guar­an­tee a mas­sive audi­ence, but it is a pre­req­ui­site. There sim­ply aren’t enough new users to make up for defect­ing ones after a cer­tain point.

Need­less to say, the debate rages on at Nielsen’s blog, at AdAge and other places fre­quented by mar­keters and media pro­fes­sion­als. Some of the com­ments are quite emo­tional, par­tic­u­larly those sub­mit­ted by Twit­ter enthu­si­asts.

Some peo­ple ques­tion Nielsen’s stats, say­ing they under-rep­re­sent peo­ple who use Twit­ter via Tweet­deck, Tweetie or other third-party tweet­ing tools. Nielsen counter-argues that as long as those peo­ple visit Twit​ter​.com at least once a month, they’re included in Twit­ter’s user base stats. (Speak­ing for myself, I hap­pily use Tweetie — but do in fact visit Twit​ter​.com at least once a week.)

Pretty much every­one agrees: the issue is not the plat­form, but how com­pelling the con­tent is to peo­ple who exchange tweets or fol­low “broad­cast tweets” by celebri­ties or those with huge num­bers of fol­low­ers.

The other key suc­cess fac­tor is whether or not the con­ver­sa­tion is stim­u­lat­ing or rel­e­vant for you per­son­ally, the peo­ple you fol­low and those who fol­low you. (This is why I argue you need a crit­i­cal mass of like-minded peo­ple to make Twit­ter’s ser­vice com­pelling.)

For me the jury is still out…