DDO's guild airship/housing has gone live on the game's test server, and players have dug up the list of rewards. All of this is obviously very subject to change (at the moment, the most efficient way to level your guild is to farm kobolds for reknown items in level 1 quests, which was not the design intent), but we're seeing enough to get some idea of what the trends are going to look like.
Guild rewards are a challenging design area. On the one hand, players are supposed to want the perks that come with being in higher level guilds (otherwise, they wouldn't really be rewards). On the other hand, guild features are supposed to enhance the guild experience and encourage players to form social ties. If the perks to guild membership are too substantial, the developers risk creating an incentive to leave your guild for the largest, least personal guild you can find, so long as they have the requisite perks.
What's on your airship?
That said, the perks in the DDO version don't look that game-altering. There are the requisite bankers, storage boxes, auctioneers, and teleports, but I've never actually felt that I was really missing these perks in the game as it stands today.
There are "crafting" stations, used to combine raid drops into raid gear, but it seems like players with access to the ingredients should be able to reach the crafting stations as well - from what I've heard, the limiting factor is raiding enough to get the materials, not actually going to do the crafting.
Finally, there are a variety of miscellaneous buffs, the most significant of which is an exp bonus that goes as high as 5%. These aren't trivial, and may be more important for players who are working on the tougher true resurrection exp curve, but nothing I'd panic over missing out on.
I'm still a bit concerned that the system as is heavily favors large guilds, which appear to have more rapid access to the most powerful rewards. Even so, if you look by comparison to EQ2, where guild rewards include teleportation to multiple locations in every zone in the game and the complete elimination of the need to harvest as a prerequisite for crafting, DDO's rewards don't feel overly game-defining.
Choices for guilds
On the plus side, low-key rewards also mean that DDO guild leaders dodge a bullet in terms of deciding what to put in their guild's limited amenity and crew slots on their airship.
If there's one thing that concerns me about WoW's upcoming Cataclysm, it's the guild talent point system. EQ2's rewards are massively significant, but there aren't that many of them, so even a small guild can quickly obtain the most game-affecting ones. If WoW's housing-less take on this type of system features more choices, and some of the choices force guilds to choose between, say, raiding and leveling alts, that could have some very unfortunate effects on guilds. Who makes that kind of choices? The officers? The whole membership? The members who contribute most to guild leveling/exp? These are tough questions that could make guild features more divisive than beneficial.