The peak of Tampa/ST. Pete market was 5 yrs ago. Perhaps you aren't refering to your friend's home in this market or anywhere in FL.
The people who make out these tax bills have a certain timing cycle for the review of their estimated evaluation for tax purposes. Don't confuse their estimated value with the actual RE market value. Sometimes they hire contractors who then suggest a revised estimation. I've seen Tax billing reflecting more than a year or two behind the changing RE market value.
Also, as far as residential RE values goes, be aware that home values in Tampa/St Pete/Sarasota went down earlier in the market correction and will come out of it a bit later. This doesn't affect you luckily as you're not selling anytime soon. Eventually it will give you a lower tax bill; however, hopefully the municipal services wont suffer'. I can't see how that can be avoided.