Facebook: Capitalize.

Facebook Fan: One who “likes” something on Facebook; capitalize (Exception: lowercase when saying “fans on Facebook”).

Facebook Page: Capitalize (Exception: lowercase when saying “pages on Facebook”).

Facebook Profile: Capitalize (Exception: lowercase when saying “profiles on Facebook”).

Facebook Group: Capitalize (Exception: lowercase when saying “groups on Facebook”).

Foursquare: “F” is capitalized; “s” is lowercase.

geolocation:
geotagging (n.), geotag (v.): One word. The verb means to add geographic data (such as longitude and latitude coordinates) to a photo or other media file.

Google: According to Google guidelines^[4], it is not okay to use this trademark as a verb. Use
search, search for, or search on instead.

handheld (n.), hand-held (adj.):
hashtag: One word.

homepage: One word.

how-to (n., adj.): Note hyphen when used as a noun or an adjective. Plural noun: how-tos. [Examples: Your How-to Guide to Home Buying (headline set in title case); Home-Buying How-To (another headline in title case)]

 i.e.:

inbound marketing: Lowercase.

internet: Lowercase.

internet marketing: Lowercase.

IT: Abbreviation for information technology. Abbreviation is always acceptable.

keyword, key word (n.): One word when referring to terms that are used on a web page to optimize it for search engines. Use two words in other cases — for example, when key is a synonym for primary or most important. (Examples: An SEO specialist can help you determine the best keywords to use on your web page. She heard little else that he said; the key word in the sentence was “love.”)

link bait:

LinkedIn: “L” and “I” are capitalized.

login (n., adj.); log in, log in to (v.): One word when used as a noun or an adjective. Two words when used as a verb, which may be followed by the preposition to. Note that sign in is preferred because it sounds less technical.

mashup (n., adj.), mash up (v.): One word when used as a noun or an adjective. Two words when used as a verb. (Examples: Anyone can create a mashup with the right technology. Use our tool to mash up RSS feeds into a single view.)