Okay, okay... I'll add in a time restriction, it won't be too hard since I'm recording the date (note, date only not the full time, though I can change that if you need it to be more exact).
One question though, how do you want to limit it? For example: Would you want to limit me to rating only 1 person a day? Or only 1 rating per-person per day?
If you really want to put a fixed limit on it now before I release the next version, let me know and I can either tell you how to edit the usertrade.php file or upload a modified one.
Second, sorry I missed your 3rd question about the top people listing... yeah, that would be very easy to do.
I'll update the main page with the to-do stuff later in the day (it's 5am here)... Looks like v1.2 already has some good features to add!