My new-to-me used bike got a tune up because it wasn't shifting well when I got it.. and it came back to me good as new. I probably could have gotten it working better on my own, but after the frustration I had getting my son's indexed shifting adjusted correctly I figured it was worth the $45 to let someone else deal with it and do it right, and check over anything else that might need attention as well. But not fulling knowing the history of that bike I figured it was important to have it looked over before I did much riding on it.

My Trek will be going in for a tune up next month since it gets 2 free from the LBS within the first year after purchase.. I bought mine in May so I plan to bring it in before that expires. I don't think it needs a tune (I think I took it in for the first free one in September or October), but I don't want to waste the "freebie"

I also agree that it's worth learning to change a tire, and having the proper tools to do so (they're cheap). As well as checking basic things like the condition of the brake pads, true-ness of the tires, tire pressure, etc - a lot of that is things you should be checking before every ride anyways. Learning to do other things like clean/lube your chain isn't a bad thing either, but it's not something you need to do all the time. A lot of LBS offer a free basic bike maintenance class, and they teach you not only how to do things like change a tire, but what to look for on your bike to keep it riding well. Some even offer advanced classes for not very much.