I got the Poker Night one in like 3 hands, haha.

25 tickets total. Probably won't get a single one more besides tomorrow's free one.

Yeah, I only have 9 - just enough to redeem the 2 prizes that were useful to me (Alien Breed 2 and the map packs for Defense Grid) plus the character pack por Killing Floor (I wouldn't spend money on esthetic add-ons). As for the big prize, Steam has millions of users, so the chances are infinitesimal anyway.

11 tickets...

I have 4, as I mostly don't care.

Man, you guys have a lot of tickets.

I have 17 currently, I'll probably finish with 19: 1 non-game achievement tomorrow, and X3: Terran Conflict... if it finishes downloading in time.

15 currently. Probably 18 or 19 by tomorrow,

I have 53 at the moment. I kinda liked the whole summer camp thing because it encouraged me to look at some interesting indie games (like Nation Red). I didn't buy that many games though since...I already went through most of Steam's catalog for the winter sale.

11, I'll probably get 2-3 more. Only have the basics and a couple of games I own. I didn't buy anything in order to get a ticket. That would be dumb.

The 'Steam Summer Camp Group' (first free achievement) has 498,837 Members right now, so you should likely assume this as the minimum number you're going to 'compete' with.
The sheer number of entries is the limiting factor here (as others have noted), not how many tickets each of them has collected.
Concerning your questions, there are people going for the full achievement set.

And personally, I have a lame 18 right now ;p

I have none, I didn't like the concept of "buy this bargain, buy that deal, buy everything we throw in your face because you weren't likely to notice its existence, spend time in front of your monitor with everything we stuff in your mouth and never bother with these crappy games again", since last year's identical contest.

I have 15 at the moment. Not a chance I would win anything, but it's fun to collect those tickets what you can.

What I don't understand is that there might be some persons who are buying those games just to get the ticket. Is there?

Got 32 now (soon 33).

I hope the next entries are offering games I already BOUGHT, and I might climb to 40

on the contrary, I looked at the achievements, and tried the demo of Beat Hazard, now I can't stop playing it.

This sale is a good idea because it gets people looking at games they wouldn't necessarily play, and some people aren't the type to buy games just for one achievement, so they'll keep playing games they buy.

It also gives you reason to re-visit games you've had for a while to add an extra little challenge.

You know, the chances of winning the games are rather low. But it would be great if someone from gog members wins 10 games :)

I've got only 8 tickets. I redeemed two gifts, and i'm fine. Im not really an achievement addict, I don't like doing achievements.