It's the feast of Our Lady of Lourdes today, which is pretty much the most respected Marian Ghost thing we've ever had. The only apparation I've ever read about was Fatima, and I don't really believe it. For the same reason I didn't believe people had the gift of tongues when I worked in a Pentecostal church, and the same reason I don't believe being 'slain in the spirit' is meaningful. To me, I guess, the issue is does something edify the church. Do people love God more because someone sees Mary and she tells them something about Russia or whathaveyou. I'm not denying it could happen, I'm just saying that 'personal revelation' (as the Church rightly calls it) has no relevance to me. It's folk Catholicism, which I've never been a fan of. There's too much in common with the Oracles at Delphi and whatnot, I prefer to stick to scripture and apostolic tradition. I have the same problem with relics. I don't deny it's efficacy, but compared to the Blessed Sacrament - God himself - what could the toe of anyone do?
Anyway, in short, I think it's best just to focus on the actual doctrines of the Church, ask for Our Lady's intercession, reverence things that ought to be reverenced (the Eucharist above all), and stick to the creeds. All the extras: medals, burying statues upside-down, etc, count me out.
...I bet now I'll have a Marian Ghost appear to tell me I'm an irreverant bastard.