I'm wondering about check-in procedures at Waterloo station for the Eurostar to Paris. Our train is at 11:40 - when should we be there? I'm wondering about immigration, security, line-ups, etc.

They tell you 30 minutes,,but I prefer to arrive about 1 hour before. You do have to have your bags scanned, go thru passport control and then find your platform position. I'd rather sit around for a bit than be rushed.

It depends. Around holidays/school vacations and long week-ends, it can get very busy. I've been there when I had to wait 20 minutes just to check in they were so mobbed (the distance between checkin and the luggage x-ray scanners isn't much, so it gets clogged there pretty easily). Other times, it was a breeze. So it depends on your date of travel. (I wonder if they will solve that problem when they move to the new facilities at King's Cross.)
Also, do you have your ticket in hand or do you need to pick it up at the station? If you have it, then 30-45 minutes is fine. If you have to pick it up at the station, at least 45 minutes (generally). You get a little more leeway if you're traveling first class. More time if you don't like your seat assignment (if you want a window seat and you get standard class tickets with seats numbered 22, 32, 52, they don't have windows, just the wall of the train).
In the waiting area, you can get snacks, bagels, drinks, newspapers, etc. (or use the first class lounge if you have a non leisure first class ticket). You can also buy a day pass for the Paris metro/bus. In the bar car, I think they still sell indiidual metro tickets if you want to bypass the ticket lines at Gare du Nord.

in addition to what BTilke mentions, in the departure lounge you can also buy the Paris museum pass, and exchange a few £ (or $ ) for € if you don't want to hassle w/ queueing for an ATM and GdNord.

BTilke, do all standard class tickets for seats ending in "2" not have a window or just the 22, 32, 52 ones you mentioned?

I don't know...I just know those were the seat numbers that I got "burned" with no-window window seats. However, looking at the seating plan shown on some web sites (eurostar's seating plan page doesn't show seat numbers), it shows those seats as aisle seats, so that, for example, seat number 21 is the no-window window seat.
I try to avoid the issue by traveling first class (leisure select). I book my ticket via eurostar.com.
The ticket agents at eurostar (before you check in) can check your seat for you and can give you a new seat assignment (if available). But doublecheck those tickets!
A couple of weeks ago, I requested a seat re-assignment, which the agent did. BUT she gave me back my old seat assignment (I didn't look at the new ticket until I was about to board the train). Unfortunately, she'd also released that seat as available, so someone showed up with the same seat assignment and I didn't know where my new seat was. I told the conducteur, who found me another seat.

On the other side, be very careful with the use of your credit card if you buy something in the "kiosk" in Gare du Nord.

This has bee the only time I have been ripped off with a cc by a cashier. She used by card card to put cash on her "moneo" card. My 8 euro book ended up costing 30

Thanks for the info, I have our tickets (unfortunatly we are in standard class) and when I get home today I'll look at the numbers on them.

BTilke - my husband and I have Eurostar tickets #51 & #52 on a train in August. Is there anyway to change them before we go, or should we just wait and show up early and try to change them at the station? I bought these through BETS which was recommended on this website and thought they would help as much as possible. I asked for, and expected, these to be window and isle seats - now after reading your posts, I'm rather dissapointed.

I have no idea if they can be changed before you go...I've never tried that. But they should be able to change them at Waterloo. You don't have to wait until the day you leave...you could pop in and change them at the station anytime (for example, if you plan to do a day trip to Windsor and take the train from Waterloo, you could do it then).
FWIW, don't get too upset. It's likely that the train won't be completely full and you can move around to another seat or, at worst, go to the bar car.
If you do change seats in person, tell the agent that you want a seat with a window and not just the wall of the train. They'll know what you mean.

BTilke, where did you find a decent seating chart for the Eurostar? I searched but so far haven't come up with much. I checked our tickets and we don't have any of the seat #s you mentioned so maybe we're ok. At least now (thanks to you) I know enough to ask when we check in!

I found one:
http://www.directline-citybreaks.co....ral/editID/301

Thanks flygirl! I compared our tickets to your plan and it looks like we lucked out and shouldn't have any "wall issues". Thanks for the link!

MOXIE...

I don't understand how that could happen....did you sign a receipt for €30 for the €8 book...don't you check the receipts???? If she ran a second charge, then she would not have your signature and it will be easy to dispute the charge and have it reversed. Makes no sense to me.