This isn't, technically, a big feature, but I expect it to make a lot of people happy. I should have done it a couple years ago.
The map's user interface for looking up historical tracking data used to only allow fetching a single UTC calendar day at a time. I've now implemented arbitrary date / time range searches, where you can select up to 14 days of track data at a time. It also allows for more exact time lookups, such as 2010-10-20 05:58:00 to 2010-10-20 06:38:00. Click the calendar icon to open up the new search form.
I've also switched to a tabbed view for the year ranges, and brought back a bit of December 2008 data. 2008 will go away over time, but the tabbed view fits at least 3 years without taking an awful lot of valuable screen estate.
The user interface still needs some tuning. The time ranges are expressed in UTC regardless of your time zone settings. The UI doesn't say that yet. It also fails to mention the 14 day limit (but it will complain with a nice red error message box if needed).
I might raise or lower the 14 day limit, depending on the amount and magnitude of server load peaks it generates. We'll see. I'd like to make it 30, but it might have some adverse effects.
How do you like it? Feedback in the comments, please!