I'm pretty sure my Premade winrate is like 15%....
I know a lot of people are disappointed with DQ from the perspective of the solo queuer, but I also have to say it kind of sucks for certain premades too.
I don't know the exact statistics (feel free to go through my match history if you'd like) but I estimate my solo queue winrate to be pretty damn good whereas my duo queue winrate is 50% and my 3+ premade winrate is like 30% at best. The problem is while my premades have pretty high individual ranks, when we play together we just suck.
http://www.lolking.net/summoner/na/32007529#ranked-stats
You can actually see that my 'main' champions that I like to play in premades (Draven/ Vayne/ Yasuo) have atrocious winrates (25%-35%?) over a LARGE number of games , but my solo queue champ pool (basically everything else) has reasonable winrates that are generally over 50% which provides a rough snapshot of how skewed premades in DQ actually is.
I'm not salty or anything or else I'd just not queue with my friends, but I feel like these games are extremely mismatched and not fun for anybody in the game - especially not the solo queuers. I actually wasn't even familiar with how fast and frequently a team can die over and over before experiencing Dynamic Queue, but now I know it's not uncommon for our team to go 30 deaths before 15 minutes, and even more commonly lose before the surrender vote is even available. I mean there are literally games where we die to a gank, teleport back, and immediately get ganked and die again in both top and mid lane and bot lane dies too because why not.
I think DQ really needs some way to rate 'synergy' of premades, because matchmaking purely off of individual MMR is really bad in my experience.