I think every developer of an MMORPG wants to figure out a way to entice players to log into their games on a daily basis. Especially new players. For the first five years I played EVE, we had the 24 hour skill queue. For veterans routinely training skills taking 7 or more days to complete, the skill queue wasn't really that big a deal. But when I was a new player, keeping the skill queue full kept me logging in every day.
The second MMORPG I currently play, Elder Scrolls Online, takes the concept to another level. ESO is a buy-to-play game with an optional subscription model and a robust cash shop. I probably should have put "optional" in scare quotes as I tried playing ESO without the sub and, quite frankly, I didn't enjoy the experience. Like many developers, Zenimax put in some pretty harsh inventory limitations for players without subscriptions. I found a subscription helps a lot.
ESO also presents players a few reasons to log in every day. I'm not referring to the daily crafting quests, although if I don't have a lot of time to play and I don't feel like doing some logistical tasks in EVE I might do some during the week. Instead, I'm referring to three benefits that, if a player logs out of the game at the right spot, are completed within 2 minutes of logging into a character.
The first two are game play features that involve, interestingly enough, playing the game. The first involves leveling my mount. Technically, the feature involves improving your character's riding skills, which ultimately involves making your character's mount better. One of the big benefits of improving your mount is increasing bag space. In a game that relies on selling inventory slots, getting up to 60 free slots is a big deal.
The second involves receiving free crafting materials in the mail. Players can spend skill points on hirelings. A feature I first encountered in Everquest 2, hirelings will send players crafting materials once every 24 hours (or 12 hours at the level 3 skill). Each crafting profession has its own hirelings. For example, I have 3 hirelings, one each for Clothier, Enchanting, and Woodworking professions. The only catch is, you have to be logged in. So if I don't log in for 3 days, I only receive one email from each, not three. Not the biggest incentive to log in, but not bad either.
The final incentive is for each time during a month, a player gets a gift. Sometimes the gift is an experience boost scroll. Other times, players receive powerful food, potions, poisons, even non-combat pets. Or gold. Potentially, lots and lots of gold. The end prize I can get for this month is 100,000 gold. To put that in perspective, I only have 52,000 gold now. At the end of the month, the list of gifts resets.
I'm not really sure how I feel about the system Zenimax settled on. I don't think the same type of system would work in EVE. The big difference is that some of the items are bind on acquire and bind to character. Also, economic gameplay is extremely limited in ESO compared to most other games I've played, let alone a free-wheeling game like EVE. But I can say from personal experience that what Zenimax implemented in Elder Scrolls Online works. I may not play every day, but I make sure to log in.