I don't do this all the time, but I regularly host 7 difficulty co-op games of 4-5 players on the weekend. Say, two weekends a month? We've even started to crank up the difficulty a little bit now - 10/10 spec ops was a total failure, but 8 was -possible-.
I try to mess around with different themed games for variety, and try to balance out the difficultly of the factions somewhat.
The one concern I have with difficulty 7 is co-op related. It varies from someone not warp gate raiding, to warp gate raiding before sufficient scouting is done (hello mk 4 raid engine two hops out!), to taking on a mark four system too soon, and letting it pour into nearby systems. My current group is fairly stable at this time of year, so those rough edges have been mostly smoothed out, we don't even need teamspeak to coordinate as much any more.
Once the expansion is final, however, and/or people have a lot more break/holiday time, I expect I'll need teamspeak again, and I expect to see a lot more mark four waves hitting me. Especially if the AI starts with Etherjets or the like. The shakedown should end up rather brutal.
I do kind of wish that on exactly AI 7 or lower (not 7.3+) raid engines were force a little further out (3 hops), and mk IV worlds (2 hops). It'd make mixed skill games a little easier to start up, while still maintaining a level of interest for the more experienced teammates. Now personally, and with a basic level of familiarity (say, 2 or 3 weekends of play), Mk IV worlds and the raid engines where they can currently spawn is entirely fine by me. I'm personally entirely fine with existing placement... and to be honest, I kind of enjoy the catastrophes that occur early in the game when someone stirs up the hornets nest.
In singleplayer I'm still sticking with 7/7.3 but mainly because I'm trying out all sorts of factions and features old and new (current masochism- advanced hybrid hives with defensive AIs, particularly Gravity Drill). Once final release hits, I'll probably try to kick it up to 8 permanently.
