When entering a ban that expires on a particular date ("Ban until" in the ACP), the end date of the ban appears to be based on UTC time rather than local time. E.g., if I put in an expiration date of 2010-11-01 for the ban, and then submit it, the ban will then show up as expiring on 2010-11-01 UTC, rather than the local forum/server time.
1) Verify that the System timezone is set to something other than UTC
2) Ban a user, selecting some future date as the expiration date by selecting "Ban (until)" from the dropdown.
3) Submit the change, and go back to the ban screen in the ACP - select the previously banned user, and notice that the expiration date is not what you specified.
In the screenshots attached, the expiration date/time is listed as 2010-07-31, 8:00 PM, not 2010-08-01 as submitted. Which makes sense if you realize that this particular server is set to US-Eastern (DST on) time, and 2010-07-31 8:00PM is therefore 2010-08-01, midnight UTC.
But if I say I want a ban until 2010-08-01, it makes somewhat more sense to base the length of the ban on the local time, rather than UTC time. Depending on where you are in the world, a ban could end up being quite a bit shorter than you intend it to be - a 48 hour ban based on the date could magically turn into a 36 hour ban instead.
Not the most earth-shattering bug, but worth fixing IMO. Keep up the good work