There has been a recent flurry of posts about why bloggers should use full text rather than excerpts in their RSS feed. These discussions can be found at blogs such as Real Lawyers Have Blogs, Sunflower Media Concepts, Burning Questions, and DennisKennedy.com.
I have always preferred full text feeds over excerpts. I figured that if a reader went through the trouble of setting up an aggregator or an RSS reader, that probably meant that the RSS reader was where they wanted to read the blog posts. I could be wrong about this, but I agree with the guys above that Full Text RSS feeds are the only way to go.