I've found +1s to be very low in comparison to other social actions. On an information site, email to a friend still leads the pack, with Twitter a close second, Facebook a low third and +1 almost non existent.
Depends on your industry though.
The relative impact comes with scale - I notice sites I +1 will jump up a page or so in SERPs for my own logged-in personalised results. Whether or not this will pass onto normal SERPs if enough people favour the same site is anyones guess, but I'd wager we're a long time off before we see any notable impact on normal SERPs yet.
IMO there's too high a percentage of SEO / Internet marketing people using +1s vs real people for the data to be clean enough for Google to filter into search results.