The differences I did notice are as follows:
- Bloglines has a bit of a "cleaner" interface.
- Google Reader has links to all your other Google services which makes for a more cluttered screen
- Blogger posts appear in one's Google Reader faster than in his or her Bloglines reader. (I just noticed this difference today, Sunday, 9/28, with Steve's latest announcement...it's already showing in Google Reader but has yet to be picked up by Bloglines.)
- Google Reader puts a date/time stamp at the top rt corner of each entry (and does the math for you, letting you know how long ago a post was written) while Bloglines dates each post under the entry. GR's method highlights newer posts.
- Bloglines allows readers either to display all posts from each feed or to show only those posted in the last hour, past 6 hours, past 12 hours, day, 2 or 3 days, week or month. This is convenient if one only wants to see the latest entries.