Is our darling headed for a rough patch? Erick Schonfeld of TechCrunch seems to think that it might be, worrying over its now  negative US user growth.

To quote:  “Ever since last summer, Twitter’s growth in the U.S. has been stalling . But in October, the number of people who visited Twitter.com from the U.S. actually declined for the first time by 8 percent month-over-month… Will the new features be enough to bring back growth in the U.S.? If they don’t, Twitter’s troubles will really begin.”

That is a quick summary, for sure, but it encapsulates his views well. If Twitter cannot reignite user growth on the website with new features, Twitter will have a hard time keeping its investors happy. Hyper growth is sexy, stagnant slow declines are not.

What can we make of Twitter’s slow down in the last few months? Recall quickly that we only have access to estimates of traffic to Twitter.com and other applications websites; we do not know if API use is growing, shrinking, or steady.

Twitter had a gigantic summer, adding millions of monthly visitors, shooting to twenty million. Then things got sticky, what happened? I have a hunch.

The people who joined Twitter in the great Oprah push, either left, or still use the web interface. The MySpace users generally use the web interface if they visit Twitter, but mostly still use MySpace. Everyone else found an application. Twitter has always been more palatable and fun via an application. Here is the metric that we need: is usage of third-party Twitter clients growing?

If we can show that, one way or the other, we will know what direction Twitter is actually moving in. There are three main segments of Twitter applications, web, mobile, and desktop. According to TwitStat, 22% of Twitter users use the web interface. That is a rather large percentage; I expect it to go down. TwitStat lists usage percentages for nearly every Twitter client ever created. Tweetie clocks in at 8.1% which just shows the popularity of the application

Seesmic, which is both a desktop client and a web client is losing traffic very, very quickly. That bodes poorly, given that you would expect it to have a strong number of consistent users to its web interface. It does not. If current trends continue, it will be visited by less than 100,000 people next month. Score one for Twitter slowing down.

Tweetie seems to be doing well. When Tweetie 2 launched, it shot to the top of the best selling app lists. People raved and raved, purchased and purchased. One point Twitter is fine.

TweetDeck, the most popular Twitter application, used by 12.5% of users according to TwitStat, is download only. Tweetdeck.com has had very consistent traffic in its life. It would seem that TweetDeck continues to do well, attracting new users. Score one for Twitter doing fine.

Another interesting metric to look at, is how the services that service tweets are doing. Take TwitPic and YFrog, two of the top photo sharing services for Twitter. Let’s take a look at their traffic levels:

That is very similar to the graph that Erick Schonfeld showed of traffic to Twitter.com. So close, in fact, that I have hard time calling it a coincidence. What does that mean? The decline in Twitter.com traffic might be emblematic to the greater Twitter ecosystem. Recall, the web interface is still the number one Twitter platform. Chalk this one up for the Twitter slowdown perspective.

Let’s look at a bright spot: Brizzly. Currently under wraps and invite only, Brizzly is growing well. Very well indeed, for a company that is still keeping the masses out. And this leads us to my point.

We have seen some larger applications struggling, some doing well, a general slowdown on the Twitter.com, and shrinkage among major utilities that Twitter users depend on. However, Brizzly shows that there is strength in Twitter yet; that dedicated users abound in droves.

Taking a step back: the people who love and use Twitter are still around, and are growing. They are using TweetDeck and Tweetie. The users that joined Twitter in the Great Hype Wave of 2009 are probably gone. Back to MySpace, Facebook or wherever else they call home.

So, is Twitter in trouble? No, Twitter is doing just fine. Twitter corporate might have some tough conversations with its investors if it cannot reignite growth, but for the regular user, Twitter is bumping along just fine.