Stoic, aloof and generally hard to read

Raincheck is a good term in many cases, a blow off is not sorry I can't I'm sick.

But don't leave it for her to call you, as a girl, I wouldn't do this, real men come and get me.

To overcome appearing aloof, remember just this one thing: smile lots! Practise smiling lots starting tomorrow in all interactions, you'll be amazed at the difference this one small change is and its easy to remember.

I have been told on numerous occasions by a variety of people, some of whom know me very well, that I am difficult to get a read on emotionally - on top of being a bit introverted and generally obtuse when it comes to flirty things. I've recently ventured back into the dating world after a hiatus and I'm afraid it might be biting me in the rear a bit. I went out with someone last week and had a good time but I'm a little worried that my general demeanor and / or my being slow on the uptake in regards to flirtations may make her feel like I'm not interested when I actually am. We are going out again this weekend, so I managed to not be a complete screw up - but I'm not quite sure how to approach things to let her know that I am, indeed interested, and not just there in body only. Is being frank and just stating the fact that I am a little slow on the uptake and am indeed interested a good way to go?

To me, what you are describing is something I have had a problem with as well. For me it is a symptom of a disorder known as Aspergers. You might want to investigate the criterion for Aspergers, and see if you match anything else. If so, it will greatly help you learn how to deal with this.

They tend to be stable, reliable, and dedicated. Harmony in relationships and home life tends to be extremely important to them. They generally withhold strong emotion and do not like to waste time with what they consider irrational social rituals. This may cause non-INTJs to perceive them as distant and reserved; nevertheless, INTJs are usually very loyal partners who are prepared to commit substantial energy and time into a relationship to make it work.

Another thing to consider is an unusual personality type which Myers Briggs calls INTJ.
Quote from the below INTJ - Wikipedia, the free encyclopedia

I forgot about the MBTI test. I took (an official) one a while back and was an INTP - but borderline on a couple of the indicators. I'll have to go re-read through that.

INTPs are quiet, thoughtful, analytical individuals who tend to spend long periods of time on their own, working through problems and forming solutions. They are curious about systems and how things work. Consequently, they are frequently found in careers such as science, architecture, and law. INTPs tend to be less at ease in social situations or in the "caring professions," although they enjoy the company of those who share their interests. They prize autonomy in themselves and others. They generally balk at attempts by others to convince them to change.
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Given their independent nature, INTPs may prefer working alone to leading or following in a group. During interactions with others, if INTPs are focused on gathering information, they may seem oblivious, aloof, or even rebellious—when in fact they are concentrating on listening and understanding. However, INTPs' extraverted intuition often gives them a quick wit, especially with language. They may defuse tension through comical observations and references. They can be charming, even in their quiet reserve, and are sometimes surprised by the high esteem in which their friends and colleagues hold them.[11]

INTPs are driven to fully understand a discussion from all relevant angles. Their impatience with seemingly indefensible ideas can make them particularly devastating at debate.[2] When INTPs feel insulted, they may respond with sudden, cutting criticism. After such an incident, INTPs are likely to be as bewildered as the recipient. They have broken the rules of debate and exposed their raw emotions. To INTPs, this is the crux of the problem: improperly handled emotions, INTPs believe, can only harm. While INTPs experience emotions as an important part of their internal lives, and sometimes share their emotions with others, INTPs nevertheless believe that emotions must not play a role in logical discussions, or be expressed in a way that would put themselves at disadvantage.