We've mentioned one way to improve the look of Windows apps in Wine, but now there's an even simpler Python script that will get your Wine apps looking native in no time.
While Wine is an incredible tool for Linux users to have, it's also a bit of an eyesore, as you're stuck with all your Wine apps looking ugly and out of place in their hideous Windows 95-style theme. This handy python script, though, will fix it up in a jiffy—just save it somewhere safe, and make it executable by right-clicking on it, hitting Properties, going to the Permissions tab, and checking the Execute tab under Owner. Now, just double-click on it, hit "Run in Terminal", and restart your Wine apps—you should notice that they look much better than they did before. Note that you'll need to re-run it every time you change your GTK theme. What's great is that unlike other solutions, this merely matches the colours of your GTK theme to Wine apps—so it isn't flawless, but it won't needlessly decrease the apps' speed like the old methods do.
Unfortunately, I don't currently have a working version of Ubuntu to test this on, but the readers over at Ubuntu-centric blog OMG! Ubuntu! seem to be getting great results, so give it a try and let us know how it works for you in the comments.