Apartment building owners call it a shadow over their industry. Renters call it a ray of sunshine. At issue is thousands of unsold condos re-entering the rental pool. In the past year, the Tampa Bay area's apartment vacancy rate has gone from about 4 percent to 7.5 percent. It hasn't been that high in three years, according to the realty firm NAI Tampa Bay. Blame the condo-conversion craze that peaked last year and left owners holding hard-to-sell units. But it's a swell time to be a renter. In Pinellas County, you can rent 1, 000 square feet in a grade A building for about $900 a month. Granite counters and stainless steel appliances? Of course.