Personally I am a little disappointed in the community.
I tried out flex for the first time last night, and had a lot of wiping on the first boss before the group eventually disbanded. There were 2 main problems:
Firstly a lot of people were dying to void zones. I am not going to be derogatory about people failing at simple mechanics, I guess we all had to learn somewhere - but there was a lot of chatter in the raid chat about finding more healers. It is difficult to get better at the game if you don't realise where the problem is and even more difficult if you don't want to know (I piped in and told the guys the problem wasn't a lack of healing, it was people standing in void zones, but they really weren't interested).
Secondly the dps was a big issue. I have ilevel 530. I recognise that my gear is more than is needed for Flex, and I am fine with the fact that not everyone in the group will be able to match my damage output. But honestly, to be doing more than double the dps of the next highest dps in the group, for someone who never got even a single piece of gear from ToT normal (or heroic) that is pretty shocking. Inspecting the people's gear revealed the obvious reason: These guys were decked out in sub-par gear. Most gear slots were filled with sub-500 items, with only the occasional sprinkling of 502/522/535 stuff. I don't think any of the other dps had more than about 500 ilevel average.
Which to me is just a little crazy. I can accept a lot of things, but seriously, it's like a bunch of unprepared, undergeared people all jumped at the opportunity to get a free ride in a raid. And the unsurprising result is that everyone lost.
I guess this isn't new to WoW. I am well used to people trying their luck at Hc Scenarios and any pug raids with totally inadequate preparation, and expectations that things will be fine. This is something I personally never do. If someone is LFM I am not going to sign up unless I believe I can carry my weight for that content. The first HC scenario I did with my DK, I destroyed all the dps in the group, because I didn't feel I was up to scratch before then.
The only difference in LFR is that LFR was designed to cater for people who aren't going to put in any effort into gearing up for raiding. So they set the barrier to entry pretty low, and then tune the content accordingly.
Flex is not LFR. It is actually meant to be real raiding. People can't just rock up half naked, with no raid experience at all and expect to waltz through it. My message to people out there wanting to do Flex pugs: Get gear. It's out there and is easy enough to obtain with a little bit of dedication. The lack of raid experience I don't mind. Flex is a great tool to learn with.
I learned a lot from last night's raid. My guild will be running Flex raids and we're going to need to pug to fill the numbers. I am going to be a bit harsh on who I let in, because it seems to me that there will always be people who try their luck instead of being a bit mature and making sure they are ready before signing up for group content.
TL;DR: I am disappointed that people aren't a bit more mature about signing up for content that they clearly aren't prepared for at all. Flex pugging really highlighted this.