Anyone have a 'move-line' function?

[Joe Smith]

I'd like a function that moves the current line up (or down) in a 
buffer. I just make do with kill/yank or transpose-lines, but sometimes 
I'd just like to hit a key and move the line, preferably without losing 
point.

As an exercise, I played with writing such a function, and I have 
something that works but it turns out to be fairly tricky to get it 
exactly right. So if there's something already done, or I've missed 
something obvious (most likely), I'll study that before I keep banging away.

<Joe