Twitter’s IPO brings attention and questions about how the social media platform does business.

Every event has a hashtag. Every company invites you to follow it on Twitter. If it’s worth saying, it must be worth retweeting. Sentences now are almost by default limited to 140 characters. Described as “the SMS of the Internet,” Twitter is one of the top 10 most visited sites on the Internet and part of nearly every digital marketing campaign. But what value does it really bring to a brand, is Twitter going to keep growing and how do companies know what they are paying for when advertising on Twitter?

This is part of the debate now taking place in the run-up to Twitter’s IPO. Launched in 2006, the company is now all grown up. While there is no price band for its offering yet, analysts estimate the company may be valued around $10-$12 billion. But the published prospectus is raising some interesting questions among pundits. These are the highlights:

• Growth: Peter Kafka and Mike Isaac of All Things D highlight that the company is growing at an annual rate of approximately 30%, but that this is nowhere near the 100% growth rate Twitter CEO Dick Costolo was aiming for. After a clear out of bogus Twitter accounts before filing, Twitter’s active user base is somewhere about 240 million. This is good, but it pales in comparison with Facebook, which had 900 million users when it went public. And of course an expansive user base is critical for driving advertising revenue.

• Churn: Twitter employees cite this as a key factor contributing to slower user base growth. People try out the service, but then stop using it. So is Twitter more niche than Facebook? Niche is not so good when it comes to attracting a big slice of advertising dollars. Attempts to launch subsidiary services to increase the stickiness factor, such as Vine (the Twitter-owned video service) and Twitter Music have had mixed results. So will Twitter be able to build more loyalty and better monetize this base?

• Revenue: Twitter started pushing ad sales two years ago and advertisers seem content to experiment on the platform. Analysts estimate ad revenue  (derived from ‘sponsored’ or ‘promoted’ tweets) could reach $900 million next year, which includes an increase from mobile advertising (65% of current revenue is from mobile ads). A Nielsen study found that users who engage with ‘promoted tweets’ have 30% higher brand favorability and 53% higher purchase intent. This looks good, but can Twitter hold on to advertisers for longer than users? Analyst Neha Dharia from Ovum says they have a long way to go.

The company’s recent acquisition of ad startup MoPub is a good strategic move. This should help exploit Twitter’s inventory and give Twitter more sway in the market.  It also gives Twitter the possibility of creating an ad network beyond its own base – perhaps sensible given concerns about growth rate. In addition, given that most of its ad revenue comes from the US despite 77% of its user base being non-US, Forrester analyst Zachary Reiss-Davis says Twitter needs to monetize better internationally and make its offerings more sophisticated for this audience.

Twitter’s IPO is the most eagerly awaited tech offering since Facebook. It’s likely to be a sure-fire hit in the short-run, but will TWTR (the proposed ticker symbol) keep soaring like a bird? Watching how its role in mobile digital marketing, and related fields like e-commerce, unfolds in the next few years will be a key factor.