Just found out yesterday too, alerted by
@srichards . This is a right pain as it was a good service.
They seem to be offering two options. Move to a small business service at 75% discount for a year (=$2.50 per month, or $30 the year), which will be relatively painless with no further re-upload required. The computer-to-computer free backup service will end however (thought this was potentially useful, but didn't use it). I didn't find out what will happen to local hard disk backups (which I do use).
The other option is to move to Carbonite for $29.99 per year. Looks like a full re-upload, and there seem to be lots of exclusions on their basic plan: no music or video files, maybe no files over 4 GB in size.
I haven't decided yet but I'll probably stay with Crashplan Pro for the simplicity, at least for a year.