I work in Minneapolis, MN and pull about 1.5mbps down on StraightTalk here with my Pre 3. It always shows the H+ symbol. I live in a suburb of Saint Paul, MN and get over 2mbps there, although a couple of times I've found myself on EDGE data with StraightTalk. It's usually right after I restart my phone and lasts only about 30 seconds before switching to H+ again.
I have NOT noticed any throttling. I also didn't see anything about data caps in the documentation they sent me.
They do send me free texts a lot (once or twice a week) to educate me on how to cash up my account.
Also, my fiancée tells me that I respond a lot faster to texts than I did with my Sprint Pre-, so it sounds like the AT&T network I use via StraightTalk is faster with texting.
I like that they let you choose to use the T-Mobile or AT&T network for the same price!