UPDATE: Although after rereading what I wrote, I realized that those people whose time means so little that they'd attend a conference largely to get the cellphone/tablet are exactly the people you don't want at the conference.
I'm attending this year again and I'm flying from Canada. No way I would attend just for the freebies. The plane is currently at close to 800$ and my hotel will be probably at least 600$. If I wanted a phone, I would buy one, it's much cheaper. And I would not miss 3-4 days of work. I love the freebies, but they would be awfully expensive if the conference had no intrinsic value for me.
It worked well for me; a friend of mine and I spent a couple Saturdays at a coffee shop ahead of the conference tinkering with the Android SDK to learn how things worked. I already had an N1, but he didn't, and so now we could actually hack together on stuff. After messing with things ahead of time I got a lot more value out of the sessions and was able to hit the ground running when I got home.
Six months ago, I would have guessed a Google TV give-away, but this year's agenda is pretty light on Google TV.
Actually, back in December they sent Google TV devices out to I/O 2010 attendees (or at least some; I received a Logitech Revue and so did a coworker of mine who attended). They did not promise this at I/O and an email just came out of the blue around Thanksgiving asking for my shipping address. So far I am disappointed with Google TV but I'm looking forward to the talk at I/O this year that pretty much is concrete evidence we'll see an Android SDK launch for it in May.
I see no reason for them to seed phones again, anyone who wants an Android phone for serious development (or anyone serious about development enough to go to I/O "just for the articles" as they say) probably would have already bought one. Tablets, maybe; I might see them doing an all-out blitz with the Honeycomb release.
The Honeycomb emulator really sucks right now and is pretty much unusable. If they want decent apps as these tablets launch, giving key developers tablet devices might be one way for Google to buy their way out of that problem.