This is of course invalid as per HTML4.01. META tags are only allowed within HEAD (just like, say, TITLE) so by putting it into a BODY, you’re essentially creating an invalid markup.
From the cursory tests, it seems that some browsers (e.g. Firefox 3.5 and Safari 4) actually put these elements into HEAD when creating a document tree. This is not very surprising: browsers are known to tolerate and try to interpret all kinds of broken markup.
Having invalid markup is rarely a good idea. Non-standard handling by browsers might lead to various hard-to-pin rendering (and behavioral) inconsistencies. Instead of relying on browser guessing, it’s best to follow a standard.
I don’t know how search engines react to such tag soup, but I wouldn’t risk experimenting to find out 🙂 Perhaps they only parse HEAD tag for certain information and will skip your BODY-contained tags altogether. Or maybe they consider these to be some malicious gambling attempts and black-list pages containing such markup. Who knows.
The bottom line — avoid this whenever possible.