Grant-funded jobs at any time have an element of risk to them, hence the term “soft money.” Sometimes the jobs last a long time (my SIL was a theoretical physicist on soft money for 18 years and then the grant went away) but sometimes they can end rather suddenly. However, if the job will be very interesting, teach you a new skill, look good on your resume, or otherwise advance your career in a direction you want to go, then consider taking the job.
As a biologist I had a number of grant-funded jobs. Most were relatively short term (6 months to three years) and all added productively to my Curriculum Vita (the academic version of a resume – it includes publications). Eventually I did land a permanent position, but the grant-funded jobs all served not only to put food on the table but also serve as a form of internship if you will. It is very common in my field for people to make a career of soft-money position.
Depending on what field you are in and where you are or are willing to go jobs may be plentiful or not. There aren’t a lot of niches open for theoretical physicists who don’t want to relocate, for example (so my SIL is still not fully employed – she is working as a tutor right now). However, another person I know works as a campaign manager and is willing to travel. She worked for Obama in California, Texas and Arkansas, then worked for a congressional campaign in Austin, and is currently working on some sort of petition drive. All are paid positions to varying degrees.
So examine your own needs and goals and consider your field.
It helps a great deal if you are single, without kids or pets, and don’t have a mortgage or a major car payment.