138 Billion Units
It has been popularly reported that Apple has more than $100 billion in cash. The amount is actually $138 billion, and the number doesn't describe cash, but instead the value of assets. Apple actually only has about $10 billion in cash. The rest is expected to be placed, for varying lengths of time, in investments. To understand what this means, we need to define a couple of terms.
When a company makes an investment with its cash reserve, it usually buys what are called marketable securities. Marketable securities are usually broken up into three categories: cash equivalents, short term marketable securities, and long term marketable securities. (A security is a thing that represents ownership of something with value. A share of a company sold on the stock market is a security, and so is a bond. The fact that a security is “marketable” just means that it can be put onto a market, like the stock market, and sold for cash.)
Cash equivalents are investments made by a company in very low-risk places that can be easily converted into cash within 90 days. These securities are considered by public investors and the SEC to be essentially cash. Apple has $10.3 billion in cash and cash equivalents.
Short term marketable securities are investments that have maturation dates (meaning the dates at which they are expected to be liquidated) within 12 months. Apple has $19.8 billion in short term securities.
Long term marketable securities are investments that have maturation dates in a timeframe longer than 12 months. Most public companies hold a large percentage of long term securities outside of the United States to avoid taxes when they mature. Apple has $67.4 billion in long term securities.
Taking the above numbers into account, and based on Apple's predictions, the company can spend $10-30 billion dollars within the next 90 days and $30+ billion dollars in the next twelve months. That leaves $67 billion predicted to be used in the far future and probably located out of the US.
UPDATE: As a user on Hacker News has pointed out, because of the economic climate, almost all of Apple's US investments could be sold immediately without loss:
Securities held by corporations as assets are shown both by type of instrument and by “intent” of the holding. In this case, the types of instruments shown on the latest 10-Q  are, as the post describes, cash and cash equivalents, short-term securities and long-term securities. But that only applies to the security itself, not Apple's intent: a 30 year government bond would be classified as “long term,” but it could easily be sold tomorrow in one of the most liquid financial markets in the world.
On page 7 of Apple's most recent 10-Q filing, the vast majority of holdings are reported to be in US Treasuries and corporate bonds, which can be liquidated immediately.
Tomorrow morning, Apple is going to “announce the outcome of the Company's discussions concerning its cash balance.” I don't think it will be as exciting as many think for the following reasons:
1. The vast majority of Apple's money is held in long term securities that are not predicted to be liquidated for at least 12 months. [See update above.]
2. A lot of Apple's holdings are being held overseas; importing that money back into the United States for any significant purchase or disbursement would create an enormous tax burden.
3. There are no strategic acquisition targets that Apple would announce publicly on a Monday morning before the market opens. Any strategic purchases would almost certainly be done behind the scenes and then described later. If Apple were to invest in Samsung's display company spinoff, it would probably not announce it to the world in a press release; it might announce it during a quarterly earnings conference call. There is precedent for this in Apple's past.
4. There are very few external acquisition targets with values in the multiple billions of dollars that would make sense for Apple. Apple tends toward vertical integration. Regardless, the most likely targets, I think, are Vizio (not likely to be announced tomorrow; it would give away their plans), Netflix (very likely), or Hulu (not likely).
Taking into account these four issues, I see two likely outcomes for tomorrow: either Apple will announce a stock buyback program, which would make a lot of sense financially (and would probably be a better investment than any of their current short term securities), or they will announce a dividend, which is something Apple has not done for a decade.
There are always the unlikely outcomes, though. And those are the most exciting.
DISCLOSURE I have positions in the following companies mentioned in this article: Apple, Netflix.