I did a web software project in the Jifty framework last year. In my experience, there was a very steep learning curve. Jifty gets a lot of things right and is quite featureful and magical; however, the documentation is lacking (boy, that was polite) and things can get a little shaky unless you do everything The Jifty Way.
Having worked through one project in Jifty, I am confident the next one would be live in 1/4 the time since I know the terrain. I'd recommend you do a sample project in Jifty before throwing your whole weight into it -- something with a similar set of features to what you want to build for real.