Dungeons And Dragons Online: DDO News: Buffing

Xundau has prodded the dev team and answered some questions about how buffs will work:

However, as some have correctly guessed, all buffs will generally be stripped when you travel to an adventure area. Still, there will be some cases where you'll be in an dungeon with people that you're not grouped with, and in these cases anyone will be able to buff you.
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In general, we are not designing DDO to be a buff-heavy game. There are some very nice buffs out there (Haste, Stoneskin, etc.), but your character won't be crippled if they don't have any buffs active.

There is more to read on the topic at the official boards. You know you want to read it.