Is it possible to import ratings into IMDB (yet)?

Depends on how it was implemented and the interface.  If it was a feature built into the site, then you would upload a list of movies with ratings in a given format, and it would:

If it found one exact name match, it would add your rating.  

If it found no match, it would report to you (give you a list at the end) of those it could not find.

If it found more than one movie with that name, it would ask you which to rate, or as above, give you a list when done of titles that were ambiguous. 

If it was a stand-along command line program, it would do the same but write the results to log file.

I dunno. I think it could find false matches too.

A few years ago I transferred my Netflix ratings (perhaps 2500-3000 of them), and it was a pain, and took many hours. It had the extra deficit of being 1-5 instead of 1-10, and I converted some into odd numbers as I went. Had there been an automated version, I never would have gone back to find those.

I hear ya there!  I have about 3400 to do as well.

Apologies but as bderoes has mentioned - there is no import functionality at this time.