Well that isn't entirely true, I can understand certain frustrations with not winning a trophy in a while, but if you take all things into consideration he has done a bang up job.
They are pretty much the only team in the premiership that have managed to actually spend less on players coming in than what has been going out, they have made profits just on their transfers.
This would be an amazing feat just for a team that was managing to scrape a living in the bottom half. To do this and never finish outside of the top 4, whilst winning trophies and the premiership on the way is pretty amazing.
I'm a United fan and personally believe that Ferguson is the best manager of all time, but whether or not he could have continued in the way Wenger has and have been as successful is very much questionable.
Yes you haven't won anything in 6 years, but that isn't really a great disgrace. You have to remember the vast amounts that Chelsea have spent in that time and United to a lesser extent. Either way all teams around and below you have lost money on transfers over the past 7 years. United included even with the massive sale of Ronaldo taken into account.
Losing Nasri and Fabregas also wouldn't seem like the end of the world to me. Nasri had one good season, well half a good season; last season. Other than that I don't think he has been spectacular. 20+ million for a player with one year left on his contract seems like good business and it isn't as if the position he is vacating isn't one you have covered in abundance.
Cesc is a slightly different story as he is great on the ball and really makes your team tick when his heart is in the game and he is fully fit. However his heart isn't fully in the game and he has had some injury problems the past couple of seasons. The last thing any team needs is an unhappy captain.
The one fault Wenger seems to have is in defence. His best defence whilst at Arsenal was one he inherited from George Graham. It was as solid of a defence as the premiership has ever seen and Arsenal have never had a defence since then that has lived up to it. I don't even think the invincibles defence was on par.
All things taken into account I can see why you're frustrated but I also think Wenger has done an incredible job for Arsenal and if he were to leave you would be a lot worse off for it.
If he can find a decent replacement for Cesc and commit to buying to premiership proven center backs, such as Jagielka, Cahill or Samba to partner Vermaelen, then you will have little to worry about.
I just think that if you take a good look at what Wenger has done and continues to do for Arsenal then it doesn't all seem like doom and gloom. Yes you capitulated at the end of last season, but before that you certainly looked good enough to win the premiership.
A couple of gritty, hard working and fully committed players added to your ranks and I personally see you as title contenders. If Wenger makes a couple of decent signings before the window closes I even plan on putting a quick 20 pounds on it.