We've been in January maybe a dozen or so times over the years. We like it...nice buzz but not crowded (obviously this year...things were very quiet).
This year we had great weather, no issues with swells, nice temperature and steady winds. We had a few days where there was a bit more wind (30 knots maybe gusting a few more)...so we just stayed in North Sound and enjoyed ONB. Very little rain over the two weeks.
Last year we had one week of mostly very high winds and big North swell and one week with very light winds and no swell! A bit frustrating in the high-winds week not to be able to snorkel, but places like Norman and North Sound are nice places to settle down with a good book and an even better Painkiller. Not much rain, just the odd squall.
The year before winds were steady the whole time, no issues with swells.
There is always the risk of Christmas winds and North Swell...but its still our favourite time to be there. Especially as January in the UK is awful!