Ok, I have an update for my previous list of Irish hosts above. I'm just finishing two Silverstripe websites hosted on MyHost.ie at the moment and I've found them to be the best to date. Silverstripe runs really well on the shared hosting accounts here so it's perfect for most clients, and I found the support service great.
I've spoken to Martin in there and they're happy to change ownership on the two folders 'silverstripe-cache' and 'assets' (so that Silverstripe can write to them without them having to be set to full permissions '777'). So at any stage after you've uploaded your files you just drop them a trouble ticket and they'll make the update.
So my vote is for MyHost.ie so far. Anyone else got any Irish hosting feedback?