Definitely. Back before kids, if I was trying a recipe I was unsure of, I'd only do 3 gallons. Sometimes, I still wish I did that - I've got two cases of not very good CAP right now
I quit doing smaller batches because my brew days a preciously few these days. If I'm going to take the time, I might as well get two cases out of it! I'll still do 2.5-3 gallons if it's something I don't really want two cases of - fruit beers, really big beers, etc. I'm still the primary consumer of my product, so if I think I might get sick of it quick - I'll do a half batch.
If you are going to do a lot of recipe scaling, I'd recommend one of the brewing softwares - BeerSmith, Promash, or BeerTools. I suck at doing the math, so I'm glad to have the computers do it for me. For me, it takes all the guess work out of brewing. None of them are very expensive. Beersmith was about $20 when I bought it. There is also several free, online spreadsheets you can use. I used this one before I went AG and bought BeerSmith: http://www.hbd.org/recipator/