It's been getting more attention in Ireland than I expect it is in UK.
My finger is not exactly on the pulse with local news (don't read print media or watch TV) but the Jackson signing was reported in the national news (Independent.ie and others on Twitter). Again, I didn't see a massive campaign targeting Diageo but I did see a few tweets from people along the lines of "Nice one Cash Converters, now lets get Diageo to see sense".
This is an Irish led campaign. People don't want him playing for anyone associated with Ireland. If he signed for e.g. Quins I don't think there would have been any targeting of their advertisers. But London Irish, nope. Also Diageo = Guinness which is such a big brand, used in tourist advertising all over the world etc. It's the Irish brand, and people don't want it associated with Jackson and his ilk.