Yo I know I'm a little late on this post, but I just joined. I spent a year hitching From Tijuana to Colombia, and did a bunch of circles along the way. I had to pay for a boat to Colombia, but not before having worked my way to the Kuna Indian islands, where the cops let me hang out and ask boats for rides. I know about the guy who got a ride for free, apparently, but it's pretty much unlikely. In fact, after him I found out that the new police at the island where he hitched the boat were not going to be so friendly to travelers of the same ilk. I felt impatient, so when a chance came to pay for a week long cruise at less than half the price, I took it.
But from those island or from Colon, you can meet boats going to Cartagena, Colombia to take you along. From the islands, there are slow cargo ships that you can board and work your way to Turbo, Colombia, but it's a long haul. The boat traffic from Colon is heaviest from right now to about the end of April. I also know that this is the best time to get a position as crew for cross-atlantic or cross-pacific rides. That's my plan, eventually.
As for hitching in Latin America, Spanish will definitely come to you, as long as you stick to the journey and not go out of your way to find english speakers. Eat anything and everything, don't worry about the damn water all the time, it's not bad in every country, only some. The hitching goes from good to bad depending on the country. In Central America hitching is fine, and Mexico too. A little slower in Panama. Costa Rica the majority of my rides were gringos, so I only stayed a week in that country.. too damn touristy and ex-patrioty, but definitely a beautiful place (I crashed a few nights in quepos) with good people.
If you want stories you can check out my buddy's at hitchtheworld.com, or mine at velabas. But really that shit doesn't matter, better to just throw yourself into the mix and let it stir you around. If you wanna chat more about it shoot me a pm. I've already hitched to the bottom of the continent and now I'm back in Lima. cheerio