To blockquote or not

From an SEO perspective, is it a good idea to use blockquotes where you're supposed to? I was thinking if you leave out the blockquote tag it might lead the spiders to think you have more original content in your post than you actually do.

IMHO it won't make any difference.

Take your content, and strip all the tags, and excess white space out. Run whatever is left through the "unique" content checker of your choice. However unique your content is, is probably what most SE indexers will think as well, give or take.