Ok, by request, I'm going to expand on this a bit. Hotel rooms notwithstanding--which I did leave from time to time, thank you Star-dude--Izmir is a place that echoes the carefree lifestyle of its home in the Aegean region.
Any trip to the city center begs for a stroll down the Birinci Kordon, the seaside boardwalk lined with inexpensive cafés and bars. Sip some wine or smoke some nargile as you enjoy the sea breezes. After your tipple, stroll on up to Konak Square and check out the clock tower, the city's symbol despite only dating from the early 1900's. Splash yourself with a bit of water from the fountain at its base. It apparently has some sort of healing powers--other than washing off dirt, I'm not quite certain.

The square also plays home to festivals and concerts, as there was when I was there on September 9th, Izmir's Independence Day.
Also coinciding with my stay was the annual Izmir International Fair, a trade and living exhibition located at the Fuar (creative name), the city's main green area. With the various fried food stands and ubitquitous product pamphlets, it reminded me of my home state's State Fair. The Fuar has a permanent folk history museum with women in Ottoman-era dress weaving carpets, an amusement park, and a zoo with heartbreakingly depressed animals. The giraffe had already eaten the leaves off of all the trees in its pen, so it was gnawing on the wire fence; the elephant had been there for 50 years; and there were "exhibits" of national mascots Sivas Kangal, the grey wolf, and Van and Angora cats. Nearly all animals were in solitary confinement, and both my boyfriend and I decided to spend little time there. Admission to the park grounds is 1 YTL; certain sections like the zoo and the amusement park have an extra nominal entrance charge.
A taxi ride from the airport to the city center should cost around 35 YTL. Havas buses regularly run into the city center, dropping off passengers in front of the defunct Grand Efes Hotel for 9 YTL. If you find yourself relying on public transit, consider getting a "Kent Kart," the local answer to Istanbul's "Akbil," which also offers discounts to city attractions such as the Fuar.
If you feel like doing a bit of shopping, check out the Kemeralti neighborhood for Taksim Pasaj-style bargains, a five minutes' walk away from the sea from Konak. For shopping more in the vein of the Akmerkez, take the Art Nouveau-style bridge over to Konak Pier, also home to great seaside restaurants.
Izmir is a sufficient weekend destination, but a longer trip might merit visiting one of the nearby beach resort towns like Foça or Çesme. I certainly felt relaxed there and didn't miss the lingering urge to deck someone that I get walking through some areas of Istanbul.