<p>I haven't been to enough of these "live" events to really determine which, if any, are worth the time / money.  Which ones do you attend and why?</p>

I used to belong to my local Linux User Group which I co-founded but I treated it more as a social event than anything else but obviously a social event full of geeks is still a great way to get a great debate going :)
Conventions and the like I've not got much out of other than being pestered by businesses who can offer me nothing that is apart from a bunch of Linux and Hacker ones where I've met loads of people who I consider friends offline, again great for the social aspect but pretty worthless to me in other respects.
That's not to say I never got any business out of attending various events it's just that treating them as social occasions meant any business that did come my way was a bonus so I never left an event feeling like it was a waste of time.