Updated Wed, Oct 01, 2008 by Medeor
Apparently you can't take it with you.
Blizzard is setting the stage for the current World of Warcraft Arena season to end and lays out what is going to happen between now and the next patch and then when Lich King ships. It appears that they will provide ample time for people to get their "PvP on" and gear up, but then it all goes away once the expansion goes live. According to Tigole:
We've revaluated certain aspects of how the arena system and current arena season will be affected during both the next content patch, and the launch of Wrath of the Lich King. For starters, the current arena season will end in respect to the ladder upon the release of our next major patch. What this means is, we'll be taking a snapshot of the current season's ladder just before the realms are taken down for patch maintenance, and our normal process will commence to determine who is eligible for the end-of-season rewards. Teams and ratings will not be wiped at that time, and will carry forward allowing players to earn points each week (and buy gear) until the launch of the expansion on November 13th. Almost immediately before Wrath of the Lich King releases, all arena teams as well as ratings will be wiped and arena charter NPCs disabled.
This is straight from the forum, so it is subject to change etc., but you can view it yourself here.
[update: And it has changed back to the standard way Blizzard handles these thing - according to Bornakk you will be able to keep honor points:
"We had hoped that the introduction of some new Honor rewards in the upcoming patch would give players a great opportunity to spend any of their remaining Honor. However, many players would still be surprised by an Honor and token reset as it isn’t something we’ve done in the past. As such, we've decided to not reset Honor or tokens upon the release of Wrath of the Lich King. Players who save their Honor will be able to spend it on level 80 rewards, although those rewards will be significantly more expensive than their level 70 counterparts.
Read it in the official area at World of Warcraft forums.]