I totally agree with the principle of a donation cap to make things a little more difficult and more interesting: however Miliband's approach is definitely putting things in a strong position for Labour to benefit.
I like the idea of opt-in not opt-out for unions, but realistically, policies to limit donations should reduce the influence of unions on Labour and the influence of wealthy funds on the Conservatives to make the fight fairer.
Also - limits to funding may give the Lib Dem's a substantially more proportionate funding, meaning they could actually run a campaign of full size and may help develop a three party system in the UK.
My verdict: Bring on the caps - as much as is necessary to make this race more interesting
I would like to see donations organised through the Unions viewed as a single donation by the organisation, rather than Milliband's proposal, which is to view them as lots of little donations, thus preserving the vast majority of his funding whilst hitting his rivals.
If it was £5k per individual or organisation, then I'd say go ahead.