As a fan of a rival basketball team (the San Antonio Spurs), I've followed Cuban for a long time. I don't really hold the fact that he's a competitor (and likes to talk smack) against him, and I'd say he's an excellent owner overall.
His complaints about the officiating are sometimes biased -- I'm not sure if it's because it helps team morale to complain about calls and make your players feel like you have their back, or just because he gets emotional about his team, which is certainly understandable enough.
Overall, I'd say he's probably the best marketing innovator in the league, though. Fans in the Metroplex have a number of different sports options and were spoiled by decades of Cowboys success, so they can be frontrunners at times and only care about their teams if they win enough to be seen as "interesting". In addition to helping make the team competitive and winning a title, Cuban has done a good job of building a strong fan base, one that isn't going to all head for the exits when they rebuild. That can be really tough to do, but he's made a lot of moves -- large and small -- over the years to make Mavs fans really invested in the teams and to make the in-arena atmosphere as fun as possible. And unlike some sports owners who are heavily involved in their teams, he knows how to hire experts at the game of basketball to handle the personnel and coaching decisions, and let them do their jobs with his support rather than feeling the need to interfere to satisfy his ego.
At first I wondered if he had any idea what he was doing given the seemingly freak success of broadcast.com (which he sold at its peak and which then fell to pieces not too long after Yahoo bought it), but over the years, he's definitely seemed like someone who knows how to make smart business decisions and bring on the right people.
I definitely wouldn't have any hesitation to do business with him, given the opportunity.