I've only flown out of BRU back to the US so my experiences may be of limited use. In my case security was pretty quick and I ended up with plenty of time to kill (I think I arrived at least 2 hrs early).

I didn't have any bags to check. No shoe removal, etc. The line moved quickly. This was in May 2010. I think from the time I got out of the taxi and to the gate area it was well under 30 minutes (on a coach ticket).

Personally I always feel better to arrive 2+ hrs for all international flights but I always worry about those things.