lost I-94W form

The US has no exit immigrations, which was clearly stated in #1. You will not be barred from leaving.
The issue is leaving and coming back. Without the turning in the form, you likely will go into the computer as having overstayed. That means you are ineleigible to return, until you convince them otherwise. If you leave for Canada even, there is no guarantee you'll be able to re-enter the country for your flight (they may not let you in under a new wavier, since you are supposed to be on the old one, which you lost), meaning there is a chance you will need to buy a ticket home that does not transit the US (which are often very expensive).

So it's your choice: stay in the US until you leave, or see your friend with the chance of major issues.

agree with #10. You will not have problems leaving the US from Boston, but trying to cross into Canada... I wouldn't risk it.
I do not know if they will let you in without your I-94W, so I would not risk it. Once you try to get back in without your I-94W, I assume they will see you are already in the country by entering you in the system, so you might have a problem there.

Exiting the country should always be possible, but reentering is risky, as others have said above.

Thanks for this guys. I'm not looking to get a new I-94W form, my trip to Toronto would just be to see a friend for a weekend, then return - all within my 90 day limit. I'm merely asking whether the absense of one will mean that I get denied re-entry into the US - and whether I won't be able to leave when the time comes, from Boston. Any thoughts?

Your I-94W is your proof that you're exiting and entering while still on the VWP. If you're entering the country without an I-94W, the border official will treat you as a new arrival, who needs a new VWP start date. One look in their computer will tell them that you did not submit your I-94W when you left the country. What happens next is up to the border official. If you're still within your 90 days, they may be lenient. If it's past the 90-day term, they'll likely assume you are an overstayer. I don't think anyone can predict what will happen.

One thing you could do is mail a plane/train ticket or credit-card receipt from Canada that shows that you exited the country. (That's what you're supposed to do when you leave the country and find out your I-94W wasn't taken from you at the border. You can either send the I-94W or other proof.) When you come back to the US, you can tell them you submitted this info. (Not sure if this will help, but at least that way you're playing it by the rules, more or less.)

One thing you could do is mail a plane/train ticket or credit-card receipt from Canada that shows that you exited the country.

Except Canada counts toward the 90 days, so a ticket or receipt from Canada shouldn't work (doesn't mean it won't, but don't rely on that).

There is only one safe option: stay in the US until you leave, then mail in your form. All other options carry with them varying degrees of risk that you may get screwed.

I see. I thought that as Canada is a country that counts towards my 90 days, I would not be leaving the waiver zone, and so I would hold on to my I-94W, enter canada, re-enter the states, and no official would pay any attention to it. So you guys really do think it's an issue, even though my passport stamp says I have like 20 days left on my waiver?

I thought the people on the waiver, within their 90 days, could hop back and forth over the canada border as much as they liked within that period, and that the I-94W was basically only used once that traveller exitted the waiver zone entirely.

Thanks for this folk, I really apreciate the tips.

I thought the people on the waiver, within their 90 days, could hop back and forth over the canada border as much as they liked within that period, and that the I-94W was basically only used once that traveller exitted the waiver zone entirely.

Correct, but this assumes that you have your I-94W.

One look in their computer will tell them that you did not submit your I-94W when you left the country

No it won't - I really doubt those I94W stubs handed in are processed instantaneously, so there must be a period of uncertainty. 'The Canadian guy took it yesterday' would probably get you back in - though no guarantee.

Hey, an update - at the Peace Bridge border by Buffalo, I told the Canadian guard that I had lost my I-94, and would it be a problem if I wanted to re-enter the states in a few days? She consulted with her American counterpart, and came back to tell me that it would be fine, I would just have to buy another I-94 for $6 when I came back. I'll let you know how that goes - fingers crossed!!!

I have two issues with your update:
1) You do not "buy" a new waiver. There is a $6 fee for using it, just as their is a $131 fee for applying for a visa. This always applies but is usually included in the cost of airline tickets, which is why most don't notice it until traveling overland.
2) I'd be highly skeptical of relying on info about entry to one country coming from a border guard from another. It doesn't mean it's not going to happen, but "the Canadian said this is what should happen" is not a valid excuse if the American denies your entry.

Either way, good luck!

lol, shit, we'll see! I leave tomorrow.....!