Well, some good news on the gas mileage front. It appears that my
Sonata is responding well to the warmer weather we've had lately (50s
and 60s). The last two fill-ups have been higher than previous tanks
and the last tank broke the magic 30 MPG mark that I've been hoping for.
I can't call a trend on two data points, but things are looking more
promising. I also just changed the oil at the 5,000 mile mark (initial
change was at 2,500) and used Mobil 1 5W-30 rather than dino oil.
Here's the mileage log thus far:

Overall
Average
Date Mileage Gallons Miles MPG MPG Notes
12/27/2005 184
1/3/2006 575 14.46 391 27.04 27.04
1/7/2006 903 11.16 328 29.39 28.06
1/15/2006 1312 15.14 409 27.01 27.67
1/26/2006 1727 15.43 415 26.90 27.46
2/5/2006 2156 14.85 429 28.89 27.76
2/11/2006 2482 12.61 326 25.85 27.47
2/22/2006 2903 15.42 421 27.30 27.45
2/27/2006 3266 13.33 363 27.23 27.42
3/13/2006 3694 15.38 428 27.83 27.47
3/24/2006 4094 14.9 400 26.85 27.40
4/5/2006 4542 15.68 448 28.57 27.52 Warmer weather
4/13/2006 5012 15.15 470 31.02 27.83 Mobil 1