I think both of you (abhred and Degs) make some excellent points in both posts.
From Degs - my take on it would be that our defensive systems seem excellent. The only really discernible 'pattern' to goals we concede is Set Pieces, errors (more later) and possibly Dropba. Set pieces we are not (and won't be by the end of the season) by any means the worst at defending them. Maybe slightly (which may be significant) worse than Utd and Chelsea. That we condede a high proportion of our goals from set-pieces is more because we're very, very difficult to break down in open play. There's also a lot of merit to the stats you bring up.
However, I do think you failed to address one concern in your analysis. Namely, the more you attack and have the ball, the less defending you tend to have to do. However, the defending you do have to do is likely to be more difficult. This is where the high profile mistakes come in. It seems to me that, compared to Utd and Chelsea in particular, we gift goals to far to many teams. Not just defensive mistakes, but real gifts, practically tied with a bow.
Both our defeats last season featured high profile own goals. I can remember us giving away a lot of stupid penalties. How often do you see Chelsea and Utd give those kinds of presents out - especially to shit sides?
Which is where I start to feel what Abhred is saying. I used to feel rock solid watching our defence, like we could repel attacks all day and night long. I actually get a bit like that, but without the satisfaction, watching Utd and Chelsea play. When we're under real pressure, I also get like that watching us...but when we're doing the pressuring it seems like we're only ever one completely self-induced defensive aberration away from borderline melt-down. Especially if it's 0-0, or our momentum has slowed and we're struggling for a 2nd. Carra and Alonso's own goals in both defeats last season, the 'we're 1-0 up with minutes to go away to a tricky Wigan team who basically can't score against any properly organised defence, let's see how many men we can pile into their box, and try hitting them with our second half competition to see who can give the ball away in the most flagrantly stupid manner' disaster.
The thing is - the bit that's been worrying me since maybe 3/4 of the way through last season - is that my worries all basically boil into one solid one, namely that our defenders aren't as good as we'd like them to be. This is also my big worry with Carra - top performance though he put in last night, considering. Our CBs are more like GK's now. Not only do they have to get involved in attacks, but they have to have peak concentration over 90 minutes. Ultimately, there comes a point where the only thing a manager can do is buy better players, hence why I say they're like GKs. If a GK makes too many mistakes, it doesn't matter how good they are at stopping shots eventually you have to get rid. It's harsh but this inevitably makes me focus on Carra - the other two are unknown quantities as a pairing, but at the same time I struggle to remember game breaking individual howlers from them. Agger's at Wigan is the obvious one, with the crucial difference that he went up the other end and basically conjured a goal for us. It's a moot point given our injuries, but it worries more all the more in the context of Carra's latest interview.
Personally, I think it's essential that Carra is rested for the odd game this season, especially against poor teams. However his comments on rotation seem very much like he wouldn't stand for that on anything remotely like a regular basis - he says what he says for all the right reasons, and I can't fault him for feeling the way he does, or the way he expresses it, but still I also can't help but think that it's a horrific position to put the manager in.
Still - Carra was, I thought, quality yesterday, made me eat my words on carrying the ball, but confirmed also that he is capable of doing a job in possession if he needs to. I'd love to see more of that over the course of the season. Maybe if Rafa bites the bullet and rests Carra before a big game maybe - then Carra comes in and has a great game, feeling as fit, sharp and confident as he has in years, he might come round to realising that the point of rotation isn't to accommodate big squads, but to keep everyone playing at their absolute best. In the long run though, I get the feeling that I wouldn't have these worries with a fit and 'fully bonded' Agger and Skrtel pairing. It's not just in possession, I certainly believe those are our two best 'natural' defenders - If either (or both together) can drill the defence as well as Carra does then, as I say, I don't think I'd be casting sickening but very grudgingly admittedly somewhat envious glances at Utd and Chelsea's (acting) captains.