Herald columnist Brian Gaynor said the 25 per cent scheme was a clever tactic as it would give the brokers and investment bankers a chance to assess how many people were interested and what price the shares might be set at.
"It gives them the ability to judge the type of interest in it. It is quite useful."
Gaynor said asking people to provide an Inland Revenue number, a bank account and proof of New Zealand residency also allowed them to get that information ready ahead of buying the shares.
Those who want to buy the shares on behalf of children or grandchildren may need time to apply for an Inland Revenue number, he said.
Share market commentator Arthur Lim said people had nothing to lose by pre-registering. The pre-registration does not require people to commit to buying the shares and no money is being requested at this stage.
Mr Lim said Kiwis had done well out of buying and holding on to previous state-owned asset sales such as Auckland Airport and Contact Energy.
"New Zealanders are under-represented in investing in shares. Mighty River Power represents a good opportunity."
It was also a chance to encourage saving by younger people, he said.
But Carmel Fisher, principle of KiwiSaver provider Fisher Funds Management, said she had concerns about the public being bombarded with marketing on the share float.
"My biggest concern is this turns it into something bigger than Texas. This is just another company on offer. It's not another Apple - it's just a power company half-owned by the Government.
"That doesn't guarantee any-thing."
Carmel Fisher said people needed to remember Mighty River Power was the first of a number of state-owned energy companies that the government was selling as well as a number of other potential share market floats being talked about.
"Don't blow it all on the first one. It's not a one-chance-only."
About 35,0000 people had registered yesterday despite the website going down at one stage.