Today, October 6th 2010, Ubuntu 10.10 is in Feature Definition Freeze, Debian Import Freeze, Feature Freeze, User Interface Freeze, Beta Freeze, Documentation String Freeze, Final Freeze, Kernel Freeze and past the Translation Deadlines in both the non-language pack and language pack editions as the release schedule details.
Basically, except for last minute bugfixes, the version of Ubuntu 10.10 you can download today is identical to the version of Ubuntu 10.10 you can download on the 10th when it gets released.
If you downloaded and installed Ubuntu 10.10 today, you would:
help find glaring issues for last minute fixing
help defray the network load on October 10th
see Ubuntu 10.10 in action without waiting
Those sound like pretty strong arguments... to me, and indeed I've been using Ubuntu 10.10 for a month now roughly. However, most people prefer to make the jump with everybody else on release day.
What are the rational reasons for that?