Marg,

Can you tell us what kind of orchid it is? I didn't read through your post from last year, so I'm not sure what kind you have.

But, I'm going to assume it's probably a phalaenopsis (moth) orchid. So, if I'm wrong in my assumption, some of this might no longer be relevant.

Anyway, I'd say aerial roots are nothing of concern with most of your epiphytic orchids (the kind that grow in bark, moss). The only thing to check really is that the potting mix is fine and the roots that are in the pot are in good condition. If the mix is starting to break down, and the covered roots are dead or diseased, your plant may be developing aerial roots because the new roots are refusing to plant themselves down in toxic conditions. If the mix and roots look good, it should be taken as a compliment that your growing conditions are warm, humid, and breezy enough for the plant to directly expose it's naked roots to you!

If your plant isn't a phal, though, and it happens to be a terrestrial species, then it might be a little more concern. If a paph is doing that, then most likely it needs to be repotted ASAP. However, there are some phrags that like to send out new growths on rhizomes that slant upward, causing the growths to develop so high out of the pot, that the roots effectively become aerial roots. So, even if your plant is terrestrial, it may not even be something to worry about.