I posed the question to the Eircom talkback forum, so we will see what they say.
When I switched from Vodafone a few weeks ago I did so because of this:

Eircom has launched a 'new' dashboard for users to check their account info. I am on the next generation broadband up to 24 megs (I get 18) and this is now on my account:

I haven't confirmed, but it looks like Eircom just dropped their cap limit on their 24 meg product by over 2/3rds. If this does turn out to be the case I will be switching back very soon.