Why May 1, 2010 vrs July 1 ?

We have been advised the following by CIRA, posted here with permission from CIRA.

My question to CIRA:
Do I (as of May 1st) charge 13% on _all_ transactions? - or -
Do I charge variable rates determined by the Registrant's listed province of record?

CIRA direction:

You may direct inquiries on how the HST transition rules and HST in general apply to you according to the CIRA information provided to us, directly to CIRA at: 1-877-860-1411

For authoratitive information directly from the government supporting CIRA's directives, please refer to the Government of Canada publication at: http://www.cra-arc.gc.ca/E/pub/gi/notice247/notice247-e.html#P1.2

Specifically, look for:

1.7 When do suppliers begin charging the HST on supplies made in Ontario or B.C.?

[...]
However, there may be situations where suppliers have to charge the HST on supplies made in Ontario or B.C. where the consideration for the supplies becomes due, or is paid without having become due, on or after May 1, 2010 and before July 2010 and some or all of the property or services are provided on or after July 1, 2010. Please refer to the questions and answers under the various headings in this notice for information on how the HST applies to transactions that straddle the July 1, 2010 implementation date.
[...]

As with all government legislation, there are other related sections dealing with the "transition rules"; you'll need to dig through the government documents to find them all.