I switched a few months ago. It's been a mixture of bad and as OK as I expected.
On the plus side, my bills are almost €20 a month cheaper, I get all my local, national and calls to 3 nominated Vodafone mobiles included in the price. My BB speed is 6mps. The wifi connection which we use on the laptop upstairs is far more stable.
On the downside, It took 3 modems before I got it working properly, I had to carry on using my old eircom netopia for a while which left me with a slow connection. The tech support is fairly slow and not much use. (though the people are very very polite and did ring me back each time as promised) Worst of all is we now have a buzzing on the landline, have done everything they suggested, moving the phone to another room, made sure all old eircom filters are removed, but it is now almost impossible to use the landline for more than a few minutes. We didn't have this problem even after switching to vodafone but still using the eircom modem so for that reason alone I intend to switch back to eircom ( on a better deal than I was) once my years contract is up.