As I stated, that cannot be the source of the delay, because getlastlogxbyname is called based on a check of quietlog before quietlog is updated to take into account .hushlogin. With the exception of step #7, all of this code is inside of a single function (main), which makes it very easy to verify that the sequence of events I'm describing is correct. (I will happily believe you, however, that getlastlogxbyname is internally now using something horrendously slow to look up that information.)
(edit: I have gone ahead and verified your statements regarding getlastlogxbyname now being based on ASL. Using that knowledge, and based on st3fan's comments about the output of dtrace, I then used dtruss to verify my own assertion regarding the order of events. The result: .hushlogin in fact only affects the output of "last login"; it does not keep login from getting that information in the first place with ASL. To keep it from doing so you must pass -q, something Terminal does not do.)
You're right. ASL is the source of the slowdown, but .hushlogin isn't actually doing anything to solve the problem.
The correct way to bypass the ASL query is to set Terminal to open shells with /bin/bash (or your shell of choice) instead of the default login shell. Terminal will still use /usr/bin/login to launch the shell, but it passes the -q switch to prevent the ASL query.
When I dug into the source code a couple of months ago, I inadvertently made both changes (Terminal settings and .hushlogin). Clearly it's the Terminal settings that solved the problem and not .hushlogin. Thanks for clearing it up.
(edit: I have gone ahead and verified your statements regarding getlastlogxbyname now being based on ASL. Using that knowledge, and based on st3fan's comments about the output of dtrace, I then used dtruss to verify my own assertion regarding the order of events. The result: .hushlogin in fact only affects the output of "last login"; it does not keep login from getting that information in the first place with ASL. To keep it from doing so you must pass -q, something Terminal does not do.)