A Sling update from one of the guinea pigs out there (me).
In general, it's worked OK but the app (I'm mostly connecting through a Roku 2) is noticeably more sluggish than others. There are occasional dropouts, but I expected that.
Last night I ran across something new to me. I'd been using it without problem earlier in the day but yesterday evening wanted to check on the Panther/Colt game through Sling/ESPN. When I navigated to the Sling app, I only received the message "You are not subscribed to any channels" (call so-and-so to subscribe). I knew that wasn't true, so I called the technical support line listed at their website. Not my choice of things to do at 9 or 10pm on a Monday night, of course. There was about a ten minute wait until someone (English-speaking) came on the line. They were able to fix it while I was on the phone with them, so in the end all was OK. But it really is a system that seems to be going through growing pains.
The guy did say they knew about Roku-specific issues that had been hitting people last night and reminded me nicely I could still connect through a mobile device (I figured that but that isn't how I want to watch TV).
I did receive my free Roku streaming stick last week but haven't had any experience yet, only enough to learn I couldn't use it through a Chromebook's HDMI port (a little bit of a disappointment, but I'm still glad to have the free stick for other use).