I also agree that saving up for a MacBook will be worth the money.
My first laptop was a Dell Vostro, which is essentially a rebranded Inspiron. The keyboard and screen were excellent. I had issues with stability (BSOD), the slow 5400rpm harddrive didn't have much kick, the trackpad sucked, and the AC port broke. Luckily, due to my warranty, they sent out a tech to fix the AC port the next day.
Next up was a Lenovo Thinkpad T400. While the trackpad was slightly better, and the laptop itself was built like a brick, the quality of the screen with subpar, I still had BSOD issues, and the overall performance seemed to degrade very quickly. Like you, I wanted some killer battery life, so I went for the 9 cell instead of a 6 cell -- basically, a larger battery that "stuck out" of the back. Brand new, the laptop was getting a solid 8 hours, but within 15 months, it was down to 3 hours. It was really, really disappointing. In addition, the default settings for the laptop being unplugged limited the power to the wireless adapter to 50%. This was buried under several menus, and caused me to have intermittent connectivity issues for the first year I owned it, until I happened to stumble upon that one setting. Lenovo didn't offer and onsite warranty, so I had to yank the harddrive out and send mail the laptop back to them to get it serviced.
Two years ago I got a 15" MacBook Pro, and I'm still very happy with it today. My battery has degraded about 10%, so I get around 4-5 hours unplugged instead of 5-7. I opted for an SSD which was a massive performance gain compared to my old laptops. I haven't had any stability issues, and my performance is just as good as the day I bought it. The only issue is that I've had two power adapter cords break on me, but with AppleCare (totally worth the money) Apple has replaced them with no problem.
In terms of running Linux, you can very easily use VirtualBox (free) or Parallels (paid) to run Linux on OSX, instead of having to boot into one or the other. This makes it super easy to try out different distros, and if you run it in fullscreen, due to OSX's Virtual Desktops, you can assign Linux to your second desktop, and literally three-finger-swipe between OSX and Linux. It's really cool if you want to take advantage of Mac-only apps, but still get to play around with Linux. That said, the 128gb SSD might feel a little cramped a year or two down the line, but it's certainly livable.
Personally, 11" is too small for me, so I'd suggest shooting for a 13". AppleCare is $249, and you can buy it any time within the first year of owning your Mac (IIRC, all Macs have a 1-year warranty). That might make it easier to purchase one now, and deal with the extra cost later.
Really, if you have an Apple store or a Best Buy within driving distance, you should try out a half dozen different laptops. The difference in quality should be very apparent.