I just bought a 2006 Civic 1.8l and was wondering the same thing. Honda sold over one million Civics in the affected years 2006 - 2008^ and there are 289 total complaints on carcomplaints, something like a .03% defect rate. Yes not every cracked block is being reported but it’s a big enough deal so that quite a few would be. But even if you said only 3% are being reported that’s still less than a 1% defect rate. And only 9 reports so far in 2018 so you get the feeling most of the weak blocks have already failed and been dealt with so your chances of getting a crack are pretty slim now over 10 years in.
At any rate after doing a little research I’m not that concerned. I still see a TON of 8th gen Civics rolling happily down the road every day so I’m guessing these cracked blocks are highly unusual and small in number. Most owners probably aren’t even aware there’s an issue. If Honda had to replace a million engine blocks they would go bankrupt and they seem to be doing just fine. Non-issue.
^Yes I know a handful of 2009 were included in the TSB. Only one complaint on carcomplaints so I left it out to keep from making the defect rate look even smaller.