Funny story:
I was only getting about 125kbps stream on my slingplayer at work, which for those who don't know...is pretty darn awful. I mean it was like MobitTV quality.
Turns out Optonline (my ISP) was capping my upload to 150kbps from 2mbps and evidently they do this if you use bittorrent, run a server or use a slingplayer.
Total. Garbage.
Luckily I looked into it and I can actually get Verizon's nex-gen FiOS installed. They don't ever cap. Ever. And I'll save $10 a month. I'm getting it installed next week at which point I'll be back up to 2mbps upload (and could go up to 5mbps with an upgrade).
So word to the wise: be careful and research your ISPs behavior on this before you commit to a Sling. DSL and FiOS people are okay as they don't cap, only Cable companies.