It seems to me a little unfair the way the daily rep boundary works from midnight UTC for users in the UK or Europe, assuming that they don't use SO every day.
If I don't access SO on a particular day (maybe it's a weekend, busy at work etc) and then use the site the following day, I may hit my rep limit in the morning and then that's it. If the boundary was midday UTC, I'd be able to amass points in the morning and the afternoon. Of course, this would only affect those users who weren't on SO every day.
This means that currently, such US users have an advantage in how many points they are likely to gain in a day over similar UK/Europe users. Unless they work into the early hours I suppose!
It would be nice if we could choose from midnight-midnight or midday-midday boundaries.