FTC was really the first big time profitable alt-coin in recent times. I started mining it a few days after it was released (quite late to the game) and I still made a decent amount. CNC was the next gold rush and I mined it right from the start. In the end I made about half as much from it as I made from FTC (CNC peaked at about half of FTC's peak price). The next coin I did well on was YAC and there I made half as much as CNC. WDC was another good coin but still smaller profits. From there on it just continued downhill.

I still mine alt-coins exclusively though, as they're still more profitable than BTC/LTC especially if you choose the right ones and buy/sell them at the right times. At the moment I'm mining and trading Digitalcoin.

This is absolutely the case. Trading alt-coins is a lot like trading penny stocks; you have to be very careful. In the specific case of MNC, a lot has been going on with it lately. Its difficulty adjustment was too slow and thus when its profitability dropped, miners moved on to the next coin in a mass exodus. This left the MNC network "stuck" with a high difficulty and a low hash rate and new coins were being minted very slowly. On May 28th a mandatory update for the MNC client was announced in order to fix the difficulty problem at block 75,000. I don't know exactly when block 75,000 was reached but it has passed and the MNC network now appears to be moving along at the proper pace. I suspect that the recent volatility of MNC may partially be in response to this, but I could be wrong. Either way, I've avoided MNC for the past few weeks as it just looks too risky for a scaredy cat like me.

Definitely take time to study the market before investing (with either your Bitcoins or your mining rig's time). Eventually you will start to recognize patterns in the markets. A few patterns that I've observed (mostly as a miner) which have served me best are these:

1. Whenever a new alt-coin is added to its first exchange, it nearly always reaches its peak price on the first day (often in the first hour(s)). This is a good time to sell out if you've already mined plenty of the coin -- even if you'd like to hold on to some. You can buy back in to the market in the subsequent days (when the coin's value is lower) and effectively double or triple your coinage if you desire. Whenever a coin that's already listed on one exchange is added to another, it usually sees a bump in price. The size of this bump depends upon the popularity of the new exchange to which the coin was added. This is another good time to sell if you need to pay your electric bill.