SpeshulEd 

With the 810, you're allowed up to 100 starred live segments. I'm not sure if that's the same on the 520, or if the 520 recognizes a segment even if it's not starred?

When you come up to a starred segment, the garmin screen changes to a map, with distance left and time behind/ahead information at the top. Last I checked, you could only have two, I can't remember if they can be edited or not...and you're stuck with the map, no other option there. The time behind information can be time behind your PR, a person's time you follow, or the KOM - this can be edited, but it defaults to person you follow or PR if no one you know has ridden that segment.

Most times it's fairly accurate, however, I sometimes get where it'll bounce from 12 seconds, to 3 seconds, to 8 seconds, to 1 second. I can't tell if its because there are multiple starred segments in the same place, or if it's picking up multiple times (your PR, your buddies best time, the KOM), or if it's just a bug and the time is way off. Of course, I've had it tell me that I'm 15 seconds off the pace at the beginning of the segment, continue to tell me that all the way through the segment, and then at the end tell me I PR'd the segment.

It works, but there are a few bugs (typical garmin). I was really excited about it when it first launched, but have since toned it down because the garmin constantly beeps at you. And although segments make great intervals, the beeping gets old when you're just trying to get to work, or focus on something else. The other frustrating thing, you notice how many stupid people made segments that end in the middle of the intersection, or require you to blow through a stop sign. And lastly, the battery dies faster. I have to charge my 810 weekly, as opposed to every other week.