Just thinking how big the market is. According to https://www.quantcast.com/top-sites/US?jump-to=110000 there are 110,000 sites with >10k monthly visitors, so I think that's the market of which they probably can get 30k users max for which they can charge $100/month on average: 30,000 $10012 = $36M/year revenue.
So for web, that's the cap it seems. According to http://www.appbrain.com/stats/android-app-downloads, there are 200,000 Android apps that have >100,000 downloads, which probably equates to 10k monthly active users, with iOS apps that's 400,000. So this will probably bring another $72M/year making it $108M revenue cap for Optimizely. So looks like the money for Optimizely is in the app market.
With 300 employees at max that's a burn rate of $15M + $25M marketing + $10M other costs, we got a profit of $58M = maybe $700M company, not bad.
Back of the envelope calculation, probably totally wrong, ok now back to work :)