Synopses are a necessary evil. You need them to query, you need them to submit to publishers. No writer I've talked to likes doing them. They're horrible.
Well, maybe not "horrible", but certainly no fun.
Really, there are two kinds of synopses: the ones you write for the book you've written, and the ones you write for the book you intend to write. Personally, the second kind are far easier for me.
This is partly because of how I outline. I usually write out about 1000-1500 words as my outline for a 100K novel, so turning that into a synopses is mostly a matter of changing it from a document only I need to make sense out of into one that any one could make sense out of. More often than not, my outlines are written in a long form already, instead of bullet points, so this essentially just an editing pass.
On the other hand, paring down a finished work down to around 1000 words? That puts me in a tailspin. Which parts are the critical things to highlight? Which can be ignored for the sake of the synopsis.
I mean, it should be easy, right: Just say what happens in the book. But it never seems that way.
Best advice I can give is to try and bring some emotional distance to it. Imagine how someone else might write the wikipedia entry for the book. What would your average reader take away as the key story points?
(This is an interesting exercise in general. I find it kind of fascinating which elements reviewers focus on-- and moreover the ones they don't-- for both Thorn and Murder.)
Is there a milestone in one's career where one doesn't have to write synopses anymore? I don't know. I'm certainly a ways away from it.
Reminder: I'm at FenCon this weekend. If you're in the area, come say hello!