If the post was made by mistake, this sounds like a great idea. However, this can then be used for other reasons too.

For example, say you have a controversial post and want to know how it will be perceived. Posting anonymously is an option, though the user gives up the right to mark it as his own. This idea would allow people to claim it if it is perceived well. That is, anonymous posting becomes an "insurance policy" against negative experience.

Second, this can lead to a malicious use, where someone posts anonymously and a second person claims it for him, say, when he walks away from his desk.

There are other cases where this can be used negatively. But, it is a good idea.

Let's examine this for a moment. There are two reasons post anonymously. One, unintentionally, such as they forgot or are too lazy to login, they followed a bad link on the site which logged them out, or they didn't have access to their password, such as if they forgot or if they are using a different browser or computer.

Two, intentional. The user wants to post anonymously.

In the fist case, making it easier for users to reclaim their post is a great idea. In the second case, reclaiming a post is more controversial, especially after any up-votes. Whatever is done--if anything at all--it must take both of thee cases into consideration.

Perhaps a user should be allowed to reclaim a post only when it has not been up-voted, no replies have been made, and it is within a certain time frame (such as 10 minutes.) This would negate a case where the user is "testing the waters". The time frame helps on a smaller scale, that is, noone took the post negatively, but noone took it positively either, which means the post can be claimed without negative impact.

Perhaps it can be taken one step further. If the time frame has not yet passed, but the post has been up-voted or replied to, the user can claim it, but not receive any positive benefits of up-votes. Also, it would be duly noted that it is a claimed post.