RRSP's, The Tax Treaty, The Mess (Information supplied on this topic is from experience only, and in no way reflects policies, regulations, or laws from either Canada, USA, Manitoba, or Minnesota).  Even though I have researched this topic for hundreds of hours, do NOT treat the below as professional advice.  I think you will find the below information, however, to be quite accurate. (Much of the information below is now OUTDATED)

General:
There is a false belief that monies held in a Canadian RRSP plans are completely safe from Uncle Sam.  After all, they are in a safe place in Canada, and we have a tax treaty to protect us from getting ourselves screwed from loosing this money.  Right?  Wrong.  The Tax Treaty, also called the "Convention" is a huge document that exists between Canada and the USA (and Canada and various other countries, and the US and various other countries).  When I refer to the Tax Treaty, I am referring to the specific document created for use between the USA and Canada.  When I refer to one being a "resident" of either country, I am using this term "for taxation purposes" only - not for immigration or other purposes.

There are 4, or possibly 6 steps that need to be completed if you have RRSP accounts in the USA come tax filing time.  Some of these steps are also needed to report general foreign accounts as well.  They are:

• Check "Yes" on Schedule "B" (Form 1040) under Part III - Foreign Accounts and Trusts
• Check "No" immediately below if you did NOT collapse any of your RRSP account (otherwise, check "Yes" if you DID collapse, or cash out on or more accounts)
• File Form TD F 90-22.1 listing ALL your foreign bank accounts, trusts, pensions, checking accounts that are held outside the USA - including your RRSP accounts
• Note: Form TD F 90-22.1 must be filed if you had any financial interest in, or signature or other authority over, a bank, securities, or other financial account in a foreign country. You do not have to file the report if the assets are with a U.S. military banking facility operated by a U.S. financial institution or if the combined assets in the account(s) are $10,000 or less during the entire year.  You must file this form by June 30 each year with the Department of the Treasury at the address shown on the form. Form TD F 90-22.1 is not a tax return, so do not attach it to your Form 1040. 
• For each RRSP or Pension account, file an "Election to Defer Interest".  There is no set government form for this election - example "elections" are shown below.  A NEW procedure was announced last year referred to as Revenue Procedure 2002-23.  This has now been replaced with Form 8891 (from 2004 to present).  This revenue procedure replaces the more confusing Rev Proc 89-45.  Previously, we had described the complicated procedures needed for this revenue procedure.  It has been greatly simplified using this procedure.
• Once you have initially filed your form 8891, for subsequent years, simply photocopy the previous year's election and attach that with your Federal return (assuming it is the "straight forward type").

Four possible situations can arise for a Canadian taxpayer, and the information that you provide with form 8891 is slightly different for each possible situation, each described below.  An election needs to be filed for each and every RRSP or Pension account (each on a separate piece of paper), each and every year for as long as you are living in the USA - or until such account no longer exists.

Straight Forward Type Election
If you have an account into which you have not transferred another account, nor have taken a distribution, use this form.

Although not explicitly mentioned in the Rev. Proc. It would be useful to indicate these on the Rev.Proc statement for that account.

Transferor Type Election
When rolling over one TRANSFEROR account into an other TRANSFEREE, one must provide a Statement on which the final total deferred income is to be indicated. This Statement must be attached to your return (unchanged) until
your the tranferEE account is eventually closed

Transferee Type Election
Any account, either new or already existing, INTO which another RRSP has been rolled, is known as a TRANSFEREE account. As well as indicating the basic information for this acount, one must also "repeat" the information from the transferOR account(s) statement. This transferOR information should remain listed on the statement every year.

Note that these statements do not cover all circumstances, however the above 4 basic statements can be "combined" to cover any of these.

Note also that this is the 1st year rhat these are being used, and any modifications, particularly arising from feedback from IRS, will be communicated here.

Conclusions:

I hope this information was useful.  Compiling it was the effort of many hundreds of hours of research, meetings, e-mails, and phone calls.  However, as stated above, I am NOT a taxation expert.  Please consider consulting with an experienced accountant familiar with taxation laws that are applicable to Canadians working in the USA.

An excellent document that you should download is called the Taxation of Canadians Living and/or Working in the United States by Mark Serbinski, C.A.