I'm in my fourth year and am trying to make a lateral move (hopefully with a few years on the clock) — presuming my partner agrees and can find something too… i've found that i've been much more successful in my applications this year (compared to 2009 when i was fresh out of grad school). I credit this year's success to having solid experience, 6 preps under my belt, and strong teaching evals (applied only to teaching schools).
i was also very forthright in my cover letter that i was *very* serious about moving. on the interviews, people have asked (esp. since i'm leaving a desirable part of the country), why would i be? i've been as diplomatic as possible when describing my current situation both in the department, but also dealing with poor state funding. everyone has been understanding and i hope that i've conveyed my serious interest to them.
from my standpoint, i'd probably be worried that you were looking again so quickly, but if you could find a compelling way to say it, i absolutely understand wanting to move. that said, it IS a lot to move and get settled and start over after only a year… it took me several semesters to catch my breath and feel like i'd gotten my classes down… so there's something to be said for sticking it out a little bit, even if you know you will apply again.
i'd guess applying in year 3 or 4 seem good — you've gotten your footing and would be able to transition to another institution relatively seamlessly… plus, i think waiting any longer and you run the risk of going past your expiration date (i.e., schools won't want you b/c they can't pay you what you're worth).