Anything up to a Python and trading is somewhat okay. T9 and anaconda is much worse since the day the beta 1.1 was launched.
There is some kind of new algorithm where if you fly a ship with a lot of cargo slots the route 'can' dive within a run or two. Doing a route in a python no problem, bring in a T9 or anaconda and bye bye profits.
To put this into a broader perspective:
1. Commodity trading behavior has remained _mostly_ stable since the first server side patch a week or two after 1.0 launch way back in December. There were some problems with background system resupply rates at launch, but that was quickly fixed.
2. Profit margins have remained stable since then. Most players with basic commodity trading "know how" can expect between 10,000 cr/ton/hour and 14,000 cr/ton/hour. Players just figuring out commodity trading will probably make <10,000 cr/ton/hour. Lucky or persistent traders can find routes of 16,000 cr/ton/hour or more, but those are either rare or short-lived, or both.
3. Rares trading also got a nerf about 1 month after launch, but it's still a dependable source of income in smaller ship. When you hit T6/Asp range it becomes a question of skill to determine whether commodity trading starts to outpace what you can earn rares trading, but at below T6 levels, rares trading is superior. When you hit T7/Clipper levels, commodity trading is superior is you can wrap your head around it.
4. Luxury trading had a brief 3-4 week window of bliss because for a while the background resupply rate of the simulation was broken and supply effectively never went down from its base level for a station.
5. With patch 1.1 (a little earlier, actually), FD clearly fixed the bug that was causing the Luxury runs to be so never-ending, and the resupply rate went back to normal. A _single_ trader with a large ship nearing 300 cargo capacity can outstrip the resupply rate, so the key now is to look for systems/commodities to have >50,000 supply, or the trade run profits won't be very stable if more than 5-10 players find it and eat up that commodity.
6. An older designed behavior called the "bulk rate tax" _seems_ to be hitting some players, but my suspicion is that they're trading in commodities that have really low supply/demand and are confusing normal price "wobble" due to supply/demand numbers <30,000 with the "bulk rate tax". However, it's possible that ships with cargo capacity above 400 are being hit by something I and other commanders cannot personally observe. I trade in a 272-ton Python, and I know another commander who trades in a 368-ton Anaconda, and we've _never_ seen the behavior that some players have been reporting as a "bulk rate tax". As for the tax itself and what it is, it's _supposed_ to affect you only when you bring a large quantity of a single commodity to a station that wants very little of that commodity. Search the forums for more.