Well, I live in Maine, and honestly, not a whole lot going on throughout the state. A few tips though:
1. If its in May it'll be rather muddy, so don't plan too much outdoors without a comfortable pair of shoes you don't mind trashing.
2. They should hit up some of the fish shacks, best seafood you'll get anywhere, especially the lobster rolls. Pass on the seafood from the big time resteraunts, three times the price and they aren't even as good.
3. Bar Harbor is a fun day of window shopping as well if you're down south, should be just opening up for tourist season in May as well, so it shouldn't be too crowded.
4. If they're into outdoors equipment the L.L. Bean outlet compound in Freeport is a blast. Freeport in general has some pretty nice outlet stores.
5. If they're driving DEFINATELY hit up the liquor stores right before the Maine border on I-95. Great selection, great prices. I stock up whenever I'm on my way back from out of state. Half gallons of Captain Morgan's Rum for about $22, fifths of Jack for $7, etc. The wine selection is nice, but the savings are in the hard stuff and beer.
6. Acadia Ntl. Park is nice for a touristy outting, for some real outdoorsing it though go to Baxter (where Mt. Katahdin is), pretty much untouched nature, great place.
7. Could always go whale watching off the coast as well, not a bad way to waste a day if you're up for that type of thing.
8. Should be some minor league baseball going on by then, the Sea Dogs are a great team to check out (Red Sox AA affiliate) since right now they're stacked with most of the best Sox prospects. Namely Hanley Ramirez, awesomely talented kid. Not sure what time of year they're running this year either, but there are some collegiate all-star leagues that run in southern Maine.
By the by, bit of general info, as a northern Mainer I don't really consider Alfred to be part of the state, more like north Mass., Maine has a pretty clear divide across the state from about Bangor. Above it you have a pretty rough, backwoods communities, below it you have the vacationland they sell for tourists. They're nothing alike and are as different as you'd imagine one state could be divided. The cultural divide is huge, enough to shock several anthropologists I know.