When users complained of delays in registering and uploading material, he replied: "Site is extremely busy. Currently thousands of user registrations PER MINUTE."
One user trying to sign up said there was "so much traffic I can't get the page to load," while others complained of pages freezing and uploads not working.
Last year's raid led to the destruction of Dotcom's Megaupload business and the loss of his $200 million fortune.
Dotcom said "When you try to stop progress, when you try top stop society for advancing, you will fail."
The Mega service is designed as a one-click encrypted file storage site with new users given 50 gigabytes of space free on sign up.
Dotcom said the ease of encryption meant internet users privacy was easily protected - even from those running the website.
Teaser screen shots of the service released before launch paid homage to year-long court battle and the legal fight to come before Dotcom's extradition hearing in August.
The shots show Mega screens holding encrypted files named "GCSB" - the intelligence agency which illegally spied on Dotcom - and "JK Evidence".
Dotcom has claimed he has proof showing Prime Minister John Key was aware of the raid before it happened, contrary to denials.
The day-long launch culminates in a party at the mansion this evening. A large stage was set up on Friday, creating speculation of a headline act ti kick off the much-hyped event.
The lead up also saw Megaupload's commercial backers emerge, along with New Zealander Tony Lentino named as chief executive.
Auckland high court files identified Lentino as the person who covered three months rent of $250,000 on the Dotcom Mansion immediately after the raid.
Dotcom has repeatedly blamed Hollywood movie studios and the music industry for pressuring the White House into ordering the raid.
On Friday, the NZ-based representatives at the Motion Pictures Distributors Association and Recording Industry Association of NZ refused to comment.
Mediaworks, which relies on commercial radio revenue, also refused to say why it had dumped a Mega ad campaign after initially agreeing to run it. Dotcom has blamed music industry pressure.
Internet NZ policy expert Susan Chalmers said there had always been a "close relationship" between the powerful Hollywood lobby and Washington DC political establishment.
She said the "rhetoric" of the Motion Picture Association of America - the studios lobby group - was "one of way, conflict and violence".
"The US is really trying to establish a uniform set of more stringent laws across the world. The White House is using this jingoistic way of describing intellectual property theft. It means the lobbyists in Hollywood are succeeding and succeeding very well."
The moves saw increasing efforts to strengthen laws in a way which did not take into account the evolving nature of the internet.
She said the design of the service appeared to ring-fence Dotcom from knowledge of the content of the files on the Mega service - a key component for any agency attempting to prove secondary copyright violation.
She said the Megaupload case and Dotcom had helped produce new case studies which defined enforcement and jurisdiction.
"He pushes things to the limit."
- NZ Herald with nzherald.co.nz
