Some websites I've noticed hardly have much on their website's homepage (i.e. google.com) where as some have a lot on their webpage (i.e. msn.com). Neither of them look good to me (google has too little for me, and msn has too much for me). Is there a way to know when you have put too much or do not have enough information on your website's homepage to look good?
It really depends on the site.
For Google anything more would be confusing and since the point is to get people to search only having a search box is a great design.
I think everyone agrees with your point about MSN being way too busy.
Each site has its individual needs and therefore needs different info on the home page.
I think the goal is to have the cleanest minimalistic home page you can get away with while still presenting your idea/company/product.
I would say the minimum information for a business homepage would answer at least some of the questions of Who, What, Why, When, Where and How. Not necessarily in that order, and not necessarily all of them at once. And in rare cases, not even at all (artistic sites). At a minimum, for business sites, you probably should cover three of those things in some form or fashion. After that, it's anybody's guess.
Google's minimalist homepage works because they really only want you to do one thing when you hit that page. They are laser-focused on search. MSN - I imagine they want you to explore, although, their problem is not so much what's on the page, but that everything has about equal weight, when they should probably do a bit more guiding.
The decisions are not always about the actual items on the page, but the informational content. And yeah, it's a judgement call based on the individual site and the client's wishes (and by client, I mean in the broadest possible sense).
Rob Walling has a periodic screencast where he reviews websites. It might represent a decent answer to your question because as people have mentioned, it's fairly specific per-site. Watching a few of his screencasts might give you enough context to have some good ideas.
37signals did a series of posts about A/B testing one of their products home page. They tried different versions including ultra short and ultra long variants. The goal was to increase subscription rates. At the end there wasn't a conclusive answer. Both versions scored higher than the standard "medium" sized page...
What I learned from their study is that the result greatly depends on the context of your own website. There so many things we don't know about our users and what moves them so It's better to do your own testing and not to rely on others' findings.
37signals' advice is to make constant changes and put them live on your website. Users will not complain if you tell them you're in the process of finding the best design for their needs. They will appreciate it actually, especially if they can express their opinion. Then the best design should come up naturally.
The answer to that is also very culturally biased, as well. There is a strong preference for suggestions, interactive content, and synchronous stuff like in-page Chat amongst East Asian websites (particularly Chinese) .. which is not the case in North America. Chinese users may expect lots of information, and variety, on their home page.
A bunch of you brought up minimalism as a design principle, which is a Western fad to a degree. http://rainfall-daffinson.com/minimalism/ .. thus not always the best idea.
For example, if you have a website that is used by five or six personas (ex. student, teacher, administrator, TA, parent, government official who may also be a parent) making a minimalist homepage will first require you to pick a subset of functions and data to deal with. ("80% rule" or whatever). Ultimately you'll end up with 6 "home pages" or "hubs", no matter how you slice it, just to get your functionality delivered. Yay?
At that point, it may have made more sense to ditch minimalism and try figuring out how to design something functionally rich and leading, get it down to 2 "home pages" (consumer and producer, for ex).
Short answer: target culture and modern design trends are important to consider. :)