Those options don't strike me as particularly strong. The assumption is that people won't mind ads in their updates, but that's something that has yet to be proven and could end up being a huge risk.

People will just move to whatever twitter like service there is that doesn't have ads.

I disagree ... once the user-base reaches a certain level, people will stay simply because everyone else is there.

Nobody moved to an ad-free social network once Facebook started placing ads.

Nobody is clicking on the ads either. When Facebook finally did do something that might make money and forced people to pay attention (Beacon) it was so odious that they had to quit immediately or people would have started moving.

I think placing ads in the content (Messages) crosses a line of irritation. Imagine if gmail started inserting adverts inside your emails when you view them. How quickly do you think people would stop using gmail?

hotmail inserts adds into my messages when I send them!

Hasn't stopped people using it.

Where "lots of options" means advertising in different forms.

Sure they can make some money from subscriptions, but Twitter is not a $50/month or even $50/year service in my opinion.

In order for Twitter to start a subscription model, they'd need international SMS (something they seem to have given up on, as third parties now provide paid SMS bundling) AND IM.

Today, I opened my T-Mo statement, and there was a Twitter ad inside. Still no IM and SMS, though. No matter how big their user base gets, that looks like a show stopper to me.

It is to some people, the 'Internet celebrity' (Calacanis etc.) crowd would gladly throw thousands/year at Twitter as it allows them to grow their image/social circle.

Those people are far too few to become a reliable source of revenue for Twitter.