Christians seem to have believed in the real presence of Christ in the Eucharist since the days of the Apostles. Granted, we don't have record of an actual Apostle discussing it, but I think there some records from the very next generation of Christians. I doubt they'd have screwed up Apostolic teaching on such a central issue of worship that quickly.
Now, one could make the case that the Apostles were mistaken in affirming a real presence and simply misinterpreted what Jesus did at the Last Supper, but that would rely on Jesus missing an important point of the very Jewish culture he was raised in. In biblical times, the holiest of holies, known as "the bread of the presence" was kept in a temple behind a curtain, where only the priest could partake of it. When Jesus spoke bread and said "This is my body." he must have known exactly how the Apostles would take it. So, if he wanted it to be taken as just a memorial and a memorial only, he would have said something to them to that affect. Now, that something may not have made the cut to make it into the bible, but the Apostles surely would have passed it on to the early Christians and they wouldn't have been saying the exact opposite within a generation or two.
So, based on what I know of history, tradition, and scripture; I really have to side with the "real presence" crowd on this one. Now, based on Jesus' use in other contexts of the term body as a metaphor and because of the evidence of our eyes and ears, I tend not to think that we're literally chewing on literal flesh and blood in the sense that we could spit out a bone or something, but I do think that Christ is present in a special way in the sacrament and did choose the words body and blood deliberately to make it clear that he was present there is a concrete and important way. Of course, there is also a very important symbolic meaning to the sacrament as well.
John
