There really is no excuse to build anything that takes a great deal of time. There is not a shortage of good, simple ideas. You are forfeiting many of the advantages of being an internet company if you are building something that can't be prototyped in weeks rather than months.
ok, but how many online to-do lists does the world need? assuming you're a hacker, if your 'good, simple idea' is easy to develop, expect to get your ass kicked by someone smarter than you in business and marketing who can pay a few code monkeys to pump it out.
good hackers get leverage and sustainable competitive advantage by solving hard problems, or at least creating software that is difficult to write. saying it's not worth building anything that takes time doesn't make any sense.
First of all, an online to-do list probably does not qualify as a good idea.
And secondly, good hackers can be hired too; it is possible to replicate most things.
I think that valuable web entrepreneurs are, in general, good hackers and good businessmen. A lot of hackers think the business end isn't important and a lot of businessmen think the technology isn't important. They are wrong. You will probably have serious competition and you need to be prepared to compete.
This isn't a kind industry. A lot of teams get crushed. Your team ought to be able to compete on both the business and technical fronts.
edit: I noticed you are one of the founders of DropBox. I don't know a great deal about your product. But, as far as I can tell we agree. DropBox seems like a straightforward, simple, focused application.
As far as I can tell, Adobe isn't an unincorporated collective of cash-strapped college students. That is an awful comparison and you should know better. Adobe is not a start up.
there are more cost effective ways of seeing what the market thinks besides disappearing into a hole and coding.