I'm taking aerospace engineering. Not really intensive on AutoCAD and other CAD programs, but it does churn well with the i7 sandy bridge
Yup, but I have went the SSD route, so now I'm on a 160GB intel 320 and storage is definitely not a limiting factor for me. Just have to manage your space well, and dump your downloads etc. into your external drives, or your desktop.
And as I've said above, it runs just fine, since most of the work is still borne by the processor, though having a dedicated gpu will definitely help to improve speeds. However the limiting factor is still your HDD, so once you're on a SSD you'll never look back, trust me.
Shouldn't be a problem. Similar to my X220 but with a built in gpu, and daily programs that I run on my X220 are photoshop, fireworks, office, premiere elements, and vegas pro. Even with 1366x768 res, photo and video editing is not a problem, just have to get used to it initially.
Honestly, mobile sandy bridge processors is a huge improvement in mobile computing, it feels snappier than my AMD x6, which in the end led me to selling off my AMD in December last year and hooted a i5 sandy bridge for my rig at home
And yes, you could go for the W520, but if for me having the same resolution and more weight is not justifiable enough for me to get the W520 over the T420. However, the weight factor of a laptop is very dependable on your preferences, so it's entirely up to you to decide. Personally I have friends who don't mind lugging around a W510 or a 17" MBP around campus day and night. Hope that helps.
Just my 2 cents