Okay, I bit. Impulsive? Not really given FFG's reputation for production quality, which I figured must be a no-brainer for something as simple as a protector sleeve. Spread over the past two days, I got my entire Arkham Horror set done: that's 998 standard, 796 mini. Considering how much AH gets played round here, a good use of between 3 and 4 hours total.
The sleeves fit quite snugly, and so some care is needed to get the cards fully seated without damage. I recommend using a rubber finger (standard kit available at any office supply). This will give you the grip necessary and protect your cuticle from being savaged by the sleeve-edge in the process I will describe.
Did I mention those sleeves are tight? "Tight as, baby!" That's a good thing: your cards aren't going to be sliding out during shuffles. It's not so convenient in terms of getting the [expletive deleted] to go in. Most cards I found would slide - stu - stu - stu - nicely in about 99% of the way. No amount of gentle edge-tapping, telekinetic force, and/or oaths you wouldn't survive swearing in the presence of your mum will get them all the way in, however.
If you gently flex card and sleeve near the opening, you can get a finger in, on the card surface and gently force it all the way down the sleeve. As I mentioned above, a clerk's rubber finger is a good idea. It will keep your nasty, oily finger print off the card, provide good traction (essential to most insertion processes) and save your fingering being repeatedly rubbed the wrong way by the edge of the sleeve itself. I didn't think about using a rubber until I was about one-third through my AH set, and I'm still hurting.
Anyway, yeah, the sleeves... Try some! Buy some! They are great!