Just read a post inquiring about a visit to the Aran Islands and whether it was time well spent. I thought biking on Inishmore would be a great day trip. I also think Skellig Michael sounds interesting but it seems that landings are not always guaranteed. I know there are nice ruins on each, but if they are similar to what we can see on the mainland, and since we are trying to cover a lot of ground in 15 days maybe I should reconsider? Please share your island experiences or recommendations.
I always feel like the best times to be on Inis Mor are AFTER the last ferry leaves and early in the morning before the first ferries arrive with all the day-trippers.
Skellig Michael and the Aran Islands travel can always be impacted by weather and sea conditions (even when it is a sunny day, seas can be too choppy for reliable ferry service although some departure ports are a bit more reliable than others). You could easily find yourself getting out to the islands with no problem, but then the weather can change while you are out there and you can't get back to the mainland. So you need to be flexible. If you are on a very tight schedule and need to be in certain towns at certain times, then a visit to the islands might not work out for you.
We went to Inis Oirr, the smallest of the islands. It is a nice size for walking. There are several things to see, O'Brien's Castle, Teampall Chaoamhan (which you could miss if you are not looking for it - nearly buried under a dune), the 1960 wreck of the Plassy, and the many beautiful stonewalls.
There are many homes that offer food and there is a pub on the island, often with music. The ferries can be a bit fluid in their pick-up times, we had to wait for 3 different ferries in order to get back to Doolin.