Nate Weiner is one of those accidental entrepreneurs who make Silicon Valley somewhat of a magical place. Back in 2007, when he was working at a design shop in Minnesota, he was so busy he didn’t have time to read or see videos he came across the web. So he did what coders do: He wrote a little Firefox extension that allowed him to save and read (and watch) the content later when he got home. A few months later, Lifehacker discovered his extension and before he knew it, the brilliantly titled Read It Later was spreading across the web.

Fast-forward to today, and that little Firefox extension has become a phenomenon. It works on most major platforms, including Android (s goog) and iOS(s aapl), and more than 300 apps (such as Zite(s twx), Reeder, Twitter, Pulse and Flipboard) have built in support for Read It Later. (In July 2011, 250 apps supported Read It Later.) For instance, if you use Flipboard to read articles, a touch is enough to save it for later reading.

Read It Later, like many of its peers such as Instapaper, is part of a growing number of save-and-read-later apps that have benefitted from the emergence of the iPad. “People are time- and device-shifting their reading because of devices like iPad,” Weiner said. I told him I love Instapaper and so do many of my friends, and he laughed and acknowledged that Instapaper is well-known with the tech audience, and as a result, has a higher awareness. He then proceeded to tell me about the past 12 months for Read It Later.

A year to remember

During 2011, Read It later added more than a million new users and at present, has more than 4 million people registered. There are full-featured clients of the service for pretty much all platforms, and that has helped the company grow with the mainstream audience.

Here are some stats to give you a better understanding of Read It Later:

• There are four saves a second, or roughly 350,000 daily saves, or about 10.5 million saves every month.
• On the iPad, the Twitter app is the number one source of “saves” for Read It Later.
• It’s the  no. 1 paid news app on Android and on Kindle Fire.
• It’s a top 10 paid news app on the iPad.

Weiner says the company has started to see growth from Android and also from the Kindle Fire(s amzn). “Android now is roughly equal with downloads we get on iOS (iPhone and iPad),” he pointed out. The Fire, he says, has been less predictable as the “downloads on the Fire have been fluctuating wildly. Some days they are higher than Android and iOS; some days they are fairly minor. There are some very large spikes on specific days (Fire launch and Black Friday for example).”

When we talked, there wasn’t much data available about Fire sales, but Weiner was still a believer in Fire. “We have every expectation that the Fire is going to continue to grow,” he wrote to me in an email. “I’m expecting to see similar download numbers from the Fire that we get on iOS by the end of 2012.”

The cash conundrum

All this growth had forced Weiner to move from “me” to “we,” as he likes to describe it. Earlier this year, with growth and increasing competition especially from the likes of Apple and Evernote (which recently launched Evernote Clearly), Weiner faced a tough choice: continue to bootstrap or try to grow the company by getting outside capital from venture investors. After wrangling with the dilemma, in July 2011, he ended up taking $2.5 million in funding from the likes of Founder Collective, Foundation Capital, Baseline Ventures and Google Ventures.

Thanks to this new cash infusion, he has grown the company to about eight people, has stopped working from his living room and has a tiny office in San Francisco. It has given him the cushion to try out new business models: something he’s currently mulling with this team and said he will make a decision about later.

I know I will be watching!