Short answer: not very much.
Ok so let’s be honest here. Most of the internet is bad at playing 40k and making lists. I’m not going to qualify that statement with any hard facts but it’s true. Recent discussion has revealed that some cool dudes still exit out there, but the vast majority of manchildren on 40k message boards like Whineseer Warseer and Dakka don’t do much but pretend to know competitive play (both are great forums with bad tactics communities).
If you ask for list advice at any wargaming message board, you’re going to get the same advice for every single army. You’ll rarely like the advice and when you change your army up and play with it, chances are it won’t perform like those cool e-bros said it would. And that’ll make you goddamned sad.

So because I’m at work and need to get this post done as quickly as possible, I’m just going to segue right into a list of my own that was poorly received over at Warseer. It’ll seem like I’m whining about people not liking it, but don’t worry — I’m not. My list rips shit UP, motherfucker. And it’s flavorful to a theme I was going for (an Imperial Fists siege beachhead force). Here’s something that was told to me. I honestly think he was counter-trolling:
You may have wins against your friends or even at local stores but at a proper Tourney you will be beaten, soundly and consistantly.
Firstly, learn to spell goddamned “consistently.” Holy fuck. If you want to be taken seriously don’t make yourself look like a rube. But that’s not what this post is about. This post is about army lists.
I beat my friends. I beat neckbeards like that guy that aren’t my friends. I play at a competitive store that hosts some of Southern California’s most competitive gamers and I fare very well — I’m not going to say I win every game but I don’t get “beaten, soundly and consistantly.” I think he was just mad because I was trolling so hard.
Now that I’ve written a bit of nerdrage, let me spin back around to the point: people on the internet are fucking stupid (especially this guy) so don’t listen to them for tactics advice. I’m not saying you shouldn’t observe the entire field and study what people think works — that is probably the best thing you can do to get better — but you should also make your own determinations about what’s good and what’s competitive.
The reason “top lists” like leafblower and stupid longfangs dudes and CAN I HAS RAZORBACK Blood Angels are so prevalent is because people are too spineless to come up with their own sort of amazing and need to feed off of something a better general did. Just remember this: statistics are stupid, mathhammer is stupid and whatever some dumb bitch on the internet tells you about your list is probably stupid.
So get out there and make the next best netlist rather than copying all of the derpy ones out there. I think you can do it.