I was going to dabble in apologetics today and started an entry on this subject, but why reinvent the wheel? There is an outstanding article at Catholic Answers regarding this particular issue.
Over time, I have heard many arguments against Catholicism that, at least initially, sound very persuasive. Upon further research though, none have panned out. For instance, many people think we worship Mary. That would be very, very wrong. One could accuse us of not worshiping the one true God if that were the case. The confusion lies in the fact we think after people are dead, they can pray for us. We're asking Mary to pray for us when we say the Hail Mary. Further, most of the words in the prayer are from the Bible itself.
Another one would be against the physical presence of Christ in the Eucharist. How can that be? How would God be more physically present in one place than in another? That's no possible. Except it is, as we see in the Old Testament when God had a special place He met with Moses upon the Ark. And let's not forget the bush. God can make Himself more physically present anywhere He wants to - because He is God.
I don't plan on spending a lot of time on apologetics on my blog, but will probably offer links or other items of interest as they come up. Diane - I haven't forgotten your entry on the Eucharist!