most do not pay unless you are super skilled 

You have to ask your employer if there is a relocation allowance. A lot of companies give one to prospective employers, but some do not.. However, if you do relocate, you MAY be able to deduct the costs on your next year's taxes. Keep all your records and receipts. 

Short answer: it depends. Like anything else, it's something you negotiate. I moved from San Francisco to Toronto (moved back to my hometown) for work. The company I was with at the time had a sliding scale for relocation based on distance (how many km from your current post to the one you're moving to), position/title, and if selling a home was involved (in my case I was renting an apartment at the time).

Going through some old receipts (it was approx. 15 years ago), my then-employer covered the movers who did everything (that alone was over $7000 (all figures CAD)), temporary housing (usually a hotel or corporate apartment/extended stay hotel) for 30 days while I looked for a place to live, they paid for one round trip 'house hunting' trip (I drove out so I'd have a car and took a $1000 payout), and a few other things I negotiated (my landlord was being uncooperative so they covered most of the cost of breaking my lease).

Covering a house sale (typically you'd need to be fairly high up the food chain) means they're covering your closing costs on the sale of your home.

Long story short...you need to ask and find out what they offer. If you work for a decent sized company this is something that would be part of your offer. One FYI: "most" companies that cover a relocation will make you sign a promise to stay at your new position/location for 18-24 months (in my case, it was a 3-year 'contract' with a non-compete clause (I could not leave to go work for their 3 largest competitors). Example: if you work for Microsoft, you may not accept a position with IBM or Apple.

The overall experience was great. My company was VERY adamant about making sure that if I needed anything to let them know. They held off on giving me a full portfolio until after my move/relocation was completed and gave me time to look at places to live (I bought a townhouse and later solid it to buy my current home).

If you have a spouse and/or kids, they "may" offer assistance with school district recommendations and/or job rec's for your spouse if applicable. Not sure? Ask.

Not many do anymore.

Some will and some will not you have to ask them not us!

Some do. It was more common in the past, but still done for high level jobs, or professional jobs that are hard to fill.

If they are going to they will mention it.

The answer is:  It depends.

Are you an executive?  How much do they give you?  A lot.  They might even buy your house.

Are you someone the company looked for via specialty recruiting? How much will they give you... Maybe $10K-$20K... money to help sell your house, pack your house, etc.

Or are you an entry level employee?  they probably aren't giving you very much at all. 

If you are in a high demand job then companies are much more likely to have relocation assistance.  They can pay moving costs, the cost to sell your house, trips to look for a new house, etc but it all depends on the company and how badly they want you and how good you are at your job.

Sometimes. Not always. Depends on how much they need you and whether there are qualified local applicants and how much money they have.