Is Interest Wrong?

This question arose while reading Proverbs 28:8.  So I checked a few of my resources, and I like what Kidner says in the TOTC volume on Proverbs about this verse.

Usury or (rsv) interest: the Mosaic law shows that the legitimacy of it depends on its context: what was quite proper in terms of economics (Deut. 23:20) was pronounced improper in terms of family care (Deut. 23:19)—as if a doctor should charge for treating his own children.

Obviously interest is a key part of society today, but there are implications/applications of this passage in terms of not taking advantage of family members (and by extension, church members) in need.  This would of course need to be filtered through the context of 2 Thessalonians 3:6-10, to avoid encouraging laziness or irresponsibility. 

On a related note, credit card companies are completely justified when they exact interest from people for making unwise financial choices.  On the other hand, perhaps they should make it harder to obtain credit in the first place.