And I completely agree that having autocomplete for lookup is really awesome. I usually do just use the browser to check it. It's silly, and I'm not going to say that I'm faster than someone using an IDE, but using an IDE just gives me too much stress.
But the most important thing by far is that I like how using a text editor forces me to really think about everything. For example, the way you order your imports, or what packages things belong in, how methods are named, etc matter much more. And I know it's silly but I find being forced to memorize method signatures enjoyable like a game of sorts, and in a way it pressures me to make sure my method/variable names are all very reasonable so they are easy to remember.
I guess I'm just not hardcore enough to go after every bit of programming efficiency! I try my best to enjoy my work =D (not that I think you don't enjoy your work because you use an IDE of course!)
It definitely adds a lot of work in having to consciously write neat code the first time around, although I also enjoy thinking about something like what ordering of import statements makes the most sense.
Anyway I'm just glad there's an option for everybody =]
Autocomplete isn't about speed, it's about context sensitive lookup in documentation. You should never have to alt-tab to a browser to check a function signature, that costs too much.