From what I've heard, they spend the background of this film setting the character up, Brock enters the storyline towards the beggining, but, venom doesn't really come into fruition until the end of this film, making him the likely villain for the fourth.
Which is good, because that means that for the next film, they'll have more of a budget for his effects, rather than splitting between another really effect-sy character (eg - sandman), and, he'll get a film focussing on him.
Of course, it'll be cool to see him at ALL.
http://www.youtube.com/watch?v=-hq-R-Nt7Fc