I just did my master / slave 2 days ago my clutch was REAL soft until my car warmed up the first time. The second my car warmed up the clutch received pressure and now its stayed nice and stiff like it should feel. Did you replace the rubber lines by any chance? did your mechanic bleed BOTH points on the clutch line?
You have to bleed the slave and than bleed the bleeder by the passenger side headlight. Read up online the order.