I've been to HAR2009 and it was the first security conference I've ever been to. It was great, it was on a camping site and there where 2000 tickets sold. I met a lot of interesting people and went to quite some cool presentations. Not all topics where technical infosec topics, but that was okay. Next conference will be BruCon and I'm looking forward to it.
I've your in the neighborhood of Brussels and want to meet nice people at a hackerspace make sure to drop by the Hackerspace Brussels (HSB). For those who don't know what a hackerspace is, just come. The people you'll meet are not the ones who'll break into your bank.