the discussion around managing email in-house vs. paying a 3rd party to do it for you, is of significant complexity, as is evidenced by the length of the original 37sig post and this comment thread.

i think it's important for each and every company to evaluate their own unique situation - the needs of their product, the resources at their disposal, the role email plays in their overall business model, their relative experience/expertise in email vs. other elements of the customer experience they are building, the maturity of the company/product, etc. it would be very unwise to make a decision on this type of matter, based solely (or predominately) on factors like "successful company X does it this way", or "successful company Y does it that way."

every company is different, and they often face this specific decision at different junctures in their life cycle.

the most useful lesson that can be gleaned from this conversation (which i've really enjoyed following), is this: as a business leader, entrepreneur, developer, etc, you have options! if you want to do it yourself, it's possible -- if 37signals can do it, so can you. but if you don't want to do it yourself, or aren't confident in your ability (for whatever reason), then there are several awesome companies out there to choose from, each of which has its own strengths and weaknesses, which puts you in the position to select the most ideal solution for your unique circumstances.

This is something that's always perplexed me. Companies copy other companies' business models and compete for the same customers all the time, but that's considered fair game. But if a design is copied, shit hits the fan.

Frankly, I'd rather someone copy my design and go after a diff niche of customers than copy my product and come after my customers.

To the guys at Curebit - ignore this noise. The focus should be on creating an awesome product, getting paying customers and generating profits. You guys have an awesome product and deserve the funding. Congrats :)

It is personally my fault for not including a credit to Highrise for the design

Lesson to us: add credits

YC gives you money, but they apparently do not provide you with advisors, handlers, lawyers or PR people who will intervene to stop you from making such a boneheaded, potentially explosive move, nor step in and help you figure out how to gracefully recover from a mistake.

You are still not planning on taking it down, just adding a credit to their site?

And, since you've admitted to stealing their site straight up - it might be "willful and deliberate", it could be considered a criminal act.

http://i.imgur.com/MXCuN.png

However, I think something that is missing is a little more guidance.  Other than the issues others have communicated, the web page showed that your company hasn't established, even in very raw form, it's own style that is best for its users.  It's normal to reflect and be inspired by others designs.  I would even recommend that you take screenshots of the design styles that speak to you.  From that point though, the screen shots should be used as "internal" discussion materials that help your company find the essence of its own style.  That style should always be taking what's best for your product/service and user base, into the style characteristics.

Once you've found your core style, express it and iterate over it using each iteration as a piece of more relavent inspiration to your style (37Signals recently released a cool video on their blog that demonstrates this process through their eyes).  The results should make you proud enough to express and share it with your customers.  Only at that point do you finally make it public.  After that keep iterating over it.  If you utilize external inspiration, make sure that you've iterated over it enough that your style doesn't feel like a knockoff.  You should be able to identify this easily and odds are, if you've been going through all this it won't be.  However, if you have concerns just take screen shots of your style and the screen shots of what externally inspired you,...show them to some people who don't work for your company and weren't involved with the design process.  They should be able to 1) pick up on your style and 2) agree that it isn't a knockoff.  Given the situation you are in, I would recommend this heavily to help give piece of mind.

I realize that you wanted to gain from the lessons learned from 37Signals internal design iteration process as well as other companies.  However, if you note what I said above, it means they were focusing "also" on their product and their customers.  Which means if you directly reflect your design from theirs, you weren't focusing enough on your customers.  You might have intended to give your customers a great design experience, but without going through the process above, your website is considered not authentic...and as a result people focus on the their feeling of "this looks oddly familiar" instead of focusing on what your product can do for them.

Many, if not all of the people who have commented have gone through their own artistic design process to build one or more designs.  And at times it can be "hell" (fun, but still) to create something that the designer feels is good enough to share/use.  It is a compliment that someone is inspired by your design.  But when it's closer to a knockoff it can make the designer feel like they sacrificed him/her-self for your free ride.  If they intended for it to be given away, then the benefit you receive gives them whatever good feeling they were looking for.  I'm sure you have, like many people, worked insane hours that took away from family, friends, and even yourself.

I hope humility, honesty, and hard work guide your company to a design that you can be proud of.