They have strong opinions
strong opinionated scientist
When most of one's time is spent poring over evidence, perfecting solutions and drawing inferences, one can safely say they have a strong opinion on most of the things us 'plebs' debate upon. These strong opinions, though, do not mean they are narrow-minded or closed. Any new evidence will be thoroughly researched upon, pronto.
They may not always be on time (Or may not turn up either)
busy scientist
They can't throw up their hands and 'call it a day' in the middle of an experiment. Also, don't forget that most scientists are also part businessmen, who manage their labs and its brand value apart from conducting research. The result? Your dinner date may get postponed quite too often. But you can't really complain if your date is a 'torch-bearer of future innovations', can you?
They need proof
scientist need solid evidence
Elaborate castles in the air may please a dreamer but not the scientist. If you are talking of news, developments or advances in the world, they better be backed with sufficient proof, or your argument may be considered invalid in no time. No proof, no opinion, Mister!
They challenge your imagination
scientists are imaginative
Is there a universe beyond ours? Can the cure for cancer be round the corner? How much more is there in the oceans to explore? Your scientist-date will ignite the imaginative corner of your mind, and you will never see the world with the same eyes again.
They like to talk about their work
scientists love talking about their work
True, they won't be super-excited to talk about their research which has been lagging due to funds, but it is truer that their subject of study is something they love more than themselves. Once they start talking of their pet project, they are bound to go on and on and on... till you either fall asleep or start taking interest, finally!
They have endless curiosity
scientists have endless curiosity
Once presented with a fact, subject or phenomenon, the scientific mind can't help but be curious about it. One moment, they see a bug on the wall, the next moment they are wondering where it came from, how it lives, right till the future possibility of it being the savior of the ecosystem. No exaggerations there.
They are disappointed by superstitious talk
scientists dislike superstitious beliefs
As minds honoring scientific temper, they may lose patience quickly by superstitious mumbo-jumbo around them. So if you mention a lot of midwives' tales, Friday the 13th stories, and zodiac compatibility accuracy, aggressive eye-rolling awaits you.
You may become a topic
scientist like thought experiments
It is a no- brainer that you may share your innermost feelings, experiences, and thought process with your date. Subconsciously, they might start thinking of it as a subject to be studied, researched, and inferences drawn upon. Go ahead, get flattered that you are a 'contribution to science'!
They may think they're smarter than you
And why shouldn't they, when they mostly are? While it may come across as borderline arrogance, win it over by your genuine care, openness, and gratitude. Smarter the date, bigger the challenge, and a more exciting relationship!
They need to examine. Everything.
scientist have an urge to examine everything
This is the only logical step after the imagination and curiosity part, don't you think? Examination, whether it be of a sample specimen or your claim that you once ate a whole jar of peanut butter in one sitting, will be examined thoroughly. Watch out!
They turn out to be passionate people
scientists are passionate people
They think deeply, devote their life to an idea and work relentlessly towards it... doesn't this all define passion perfectly? With a little more understanding of each other and patience, you will discover that you make a passionate pair of lovers. Cheers to that!
You'll always learn something new
scientists keep teaching you something new
Not just their own project, they love to talk of all the buzz in the scientific world. You will regularly come across the latest updates in science, whether it be the discovery of the Higgs-Boson particle or the debate on genetically modified crops. Take notes.
They see the big picture
scientists see the big picture
Petty differences in normal relationships can be avoided when your date is the one who sees the inherent connections in all things around us. So don't mind if they don't notice your new hairstyle... they may be busy seeing you in the same frame of a happy future together.
They bring out your inner nerd!
scientists bring out your inner nerd
Were you putting away those books and acting all glam just so that you aren't left out of the current crowd? You might just have found a person who doesn't want you to hide behind that facade. Pull out your geeky glasses, carry books to your date or talk of constellations on a stargazing date - you will not be judged (in fact, be appreciated).
Know your Star Wars, Star Trek, and Doctor Who trivia thoroughly
know your sci-fi trivia around scientists
Oh, and the most important one, know that your proposal will be rendered invalid if it isn't in Klingon.

I am serious.