This was our first extended stay use of Airbnb, and we thought it was GREAT. Having an apartment rather than a hotel room when staying for several weeks as we did (probably even staying for a week) was just wonderful. Felt like we were coming home each night, and the luxury of a kitchen, as well as a living room, was outstanding.
Galenya couldn't have been more helpful (and was incredibly gracious when a misunderstanding had her sitting in the apartment waiting for us on the wrong day!) or more responsive throughout our stay. We felt that if there were any problems or questions, she was always available to help with solutions. The apartment, particularly the bedroom, was a bit smaller than we'd expected, and the apartment (and building) was quite old (and the wooden floors certainly creaked), but it was charming and everything worked fine. Perhaps more important than expected, the shower was great (we'd chosen this apartment over a particularly attractive one on Ile St Louis because that one only had a tub), even though the hot water did occasionally turn cold, it was no big deal, and 20-30 seconds later it was back in business. Also, having a washing machine was a huge help!
I suspect there is no ideal location central to all of Paris, but it was ~45 minute walk to the river and most of the museums/gardens/etc along it. But was a really nice walk, and when we didn't want to walk (or went further out), the apartment is very close to two subway stops, from which you can easily get to anywhere!
We thought this was a great value, a great apartment, and a great experience