I usually do a fair bit of research before speedying anything. Google it, look at the page history, etc. I delete far more than I remove tags -- in fact I rarely remove tags, unless the cited CSD clearly doesn't apply.
Why? Because sometimes I half-agree with the tag, but don't think that the cited CSD is fully met by the article. Maybe in spirit but not in letter. So I just leave the article as it is, hoping another admin can come to a decision.
I don't generally do any research when patrolling CSD. The criteria are all such that you can judge based just on reading the article. (Except for copyvios, I suppose, you have to read the thing it was allegedly copied from too.) For example, an A7 deletion doesn't require you to determine notability, it just requires you to see if the article makes any assertions about notability, which is quite easy and doesn't require any research.
Out of 10 CSDs I probably delete 6 or 7, remove the tag from 1 or 2 and leave the rest for another admin because I'm not sure (that's the good thing about a wiki - you can just move on and let someone else deal with it if you aren't sure what to do). The tags that I remove are generally A7's that probably aren't notable but do make assertions of notability and should probably be PRODed rather than speedied (I don't generally add the PROD tag, since that would require research and I don't want to take the time required to do that properly).