NickTee

If you're looking for good gas mileage, don't bother with a IS250. The TSX has "plenty" of power and still gets great gas mileage. I usually averaged around 31 mpg doing mixed driving, highway driving was usually 75-80mph. It drove nicely, handled well enough, and it was a great car. The rear seats also folded down, so I could fit longer things if needed.

While the 2nd gen IS is a step above the TSX, it's really not that much better. The IS250 also felt slow, almost as slow as the TSX(quarter mile shows they are fairly close and my ES350 DD has beaten several IS250s), but you're looking at way worse gas mileage. While someone may bring up the argument of handling, the limitation of most vehicles is located in the driver's seat and the TSX is quite competent with a good driver.
The IS350, on the other hand, was much peppier and handled well like the IS250(but the IS250 is slow). If you're looking at the IS family, I wouldn't bother with a 250, because at that point might as well go with a TSX in order to get much better gas mileage and save money. You also won't have to hear people telling you that you should have gotten the IS350, which is an added bonus.

Final thoughts: get a TSX for great gas mileage or a IS350 for a fun car that gets IS250 gas mileage. Bullocks on the IS250(sorry IS250 owners, they're just not that great. I'd sooner buy a cheaper Miata or RX-8 for track/Auto-X purposes).

Bichon

You would be right that your gas prices are the highest in the country -- more than a dollar/gallon higher than the national average, but only a small part of that is due to the cost of living. It's mostly due to California state taxes (CA fuel taxes are 34 cents a gallon more than what we pay in NJ) and the special "boutique" fuel blends that California clear air regulations require -- which are significantly more expensive to refine.

datis250

Yes you are very correct. I was thinking it over a lot, and considering the 250 also has the carbon build up issue, it makes me very skeptical to buy it. And I'm already being told from friends "hey why don't you buy the IS350" LOL. For me I think the TSX is overall better for my needs and for the reliability I need. Unless of course I decide to buy the IS350 but the price is stopping me. But the lexus has the killer style, and the mods are crazy sick for my likings.

And you guys complain about gas LOL. Come up to Canada bro, i mean i don't know how we fair up against the Cali guys, but our gas is plenty expensive compared to you guys!

20LS01

I had a 2006 tsx for about 45k miles but my now my sister drives it. I just bought an is250 last week.

Gas Mileage:
My tsx averaged about 28-29 mpg with mixed driving. 75/20 hw/city. It always went about 350-390 per tank before the gas light went on(13.x gallon fill up). The highway mpg is excellent(32+ all the time) but once you start driving in the city, mpg takes a nose dive. These cars suck up a lot of gas in the city. In purely highway driving, i gotten 500+ per tank before(Vancouver, BC back to SF, CA). I think i averaged 35mpg that tank.

I had my is250 for a week now and ive put on 130 miles on it. The computer is telling me that I am getting 26mpg. This is with 60/40 highway/city. I am at 130 miles at the 3/4 mark on my gas meter. I am optimistic about this car getting close to 30 after i learn how to drive it and perform maintenance to enhance mpg.

As far as driving, here are my thoughts.

Drivetrain:
Is250 has a smoother engine and transmission. It has better low-end torque for city driving. The tsx is no slouch either but you have gas it slightly more to get it moving but once it gets to 3k rpms, it takes off and it REALLY takes off when vtec engages. Overall, i prefer the is250 drivetrain for it's smoothness. The tsx transmission shifts quicker and responds to downshifts better. Oil changes will be more expensive on the lexus as it requires 7 quarts whereas the tsx requires 5quarts. Both can take regular or synthetic oil.

Suspension:
I prefer the TSX suspension more than the is250. It feels more cush and more responsive, but then again. i had 22mm progress RSB. With the RSB, TSX cornered fairly flat and responded very well on turns. My is250 feels bumpy and doesnt seem to absorb potholes and bumps as well. Looking to add the f-sport rsb shortly. The is250 feels as bumpy as my lowered integra koni/GC rocking 350/250 spring rates.

Refinement:
As people have stated, the is250 is more refined inside. There is a higher level of detail in this car. The tsx is more spacious for both the driver and passenger. IS250 is quieter inside as well, but not by too much. No fold down seats on the is250 but there is a fit through hole on the is250 for skis, fishing poles, etc.

The tsx now has 75k miles on it and has been flawless. Only had to replace the driverside door lock actuator. I did it myself for 20 bucks. Just feed it gas, change the fluids and filters and it will literally drive you around the earth many many times. Someone had warned about transmission issues in the tsx, that is not the case for this car. it has a solid reliable transmission. Just make sure to drain/refill with honda atf every 30-45k miles and it will last a while. I think the tsx in the long run will be a more reliable and less expensive car to own. I like the is250, but too early to really know how i feel about. So far, it's good minus the space available if you were to carry back seat passengers all the time.