I don't suppose the Jonathan Bailey, proprietor of PlagiarismToday would find it funny if I reproduced his entire post below. Anyway, most blogs can't survive without content referenced from other sites. However, there is a fine legal line between referencing and ripping off:

In lieu of a hard and fast rule, much like the fair use provision itself, we begin to seek out a framework for determining if a reuse is ethical or not. This framework would contain the following elements, many of which are found in the standard fair use provision:

1. The amount of reused content compared to the amount of original content.

2. The amount of reused content in relation to the original work.

3. The frequency with which large blocks of text are used.

4. What is gained by the original author.

5. Whether permission was granted in advance, either through a CC license or direct permission.

6. Whether attribution was provided or not.

7. Other indications as to the intent of the one reusing the work, including excessive advertisements, links to one’s own sites and other forms of profiteering or over the top promotion.

Read on if you are interested in copyright law or just have a blog and want to make sure you're walking the line.