To Invest £70k, here is what I would encourage you to think about.
Going back to the original point, what every investor wants is to be able to add the maximum added value to what ever asset or entity that they purchase. Whoever said balance or diversification is half right, you could do this or put all your eggs into one basket and watch like a hawk! I do diversify, but often lament its easier in terms of time overheads to for example buy more flats or houses in the same area because it saves on time over heads.
Here is my 2p worth:
1a. Property - pain the arse at the best of times. But as people have mentioned, the value cannot just plummet to zero if properly insured. Its a good place to store wealth but I don't like it to make money money from. Taking the B2L example, if you can get a very good clear yield - i.e. double digits then you should make around 5%. Its not brilliant and is very continigent on cheap lending continuing.
1b. Property - as first time buyers struggle landlords are buying small family homes and some of these are getting very good rents esp in south east and in/around london. Read: double digit yields.
1c. Property - make friends with your lawyers - I've sued more people over property than just about anything. Its messy and nebulous sometimes over who owns what and is responsible for what. But on the positive side property rights are probably on the main much more defendable compared to say domains or other IP.
1d. Property - get good people to manage it and do be afraid to ask and re-ask the same question of different people until you have the costs under control. You might need to try different management agents until you find people you can trust who won't "spunk" your money away or try and rip you off. This is where I advocate splitting down the jobs, so you use different companies for each part of the process and again this is where economy of scale comes in - managing 5 is not that more hassle 1 if in the same area and managed by the same teams.
2a. Shares. You can get 14% dividends and chose the sector. For example for could try some of the very high paying REIT's (Real Estate Income Trust) for example that would give you exposure to the property market without some of the management risks of actual property.
2b. Shares - Buy what you know. Something you don't mind tracking on a daily basis and that you think has long term "legs". Here you are expected to take a punt on the future.
2c. Shares - Build a portfolio based on your needs now and the future. Capital growth vs. income? What is more important? Ideally you should mix assets that pay dividends and others that will benefit from CG (rise in share price).
2d. Shares - There are as many asset class as there are people. Its a minefield of diferent products - so choose something you feel comfortable. If you are new to shares, consider easing yourself in gently and dropping a small amount into the markets in regular intervals to give you a feel for equities.
2e. A FTSE tracker can give you around 5% dividend without taking any risk on actual equities individually. Probably you will find some schemes on the FTSE All share - sadly not the FTSE 100. Virgin Money do-one. Or you could buy the ETF (Electronic Traded Fund) through your broker. See here:
http://www.google.com/finance?q=LON:ISF
3. Domains/Web property - I won't comment just now.
In summary, I would try to make as few transactions as possible and to look ahead for 5/(your time frame) years and try to hold those assets long enough such the cost of the transaction is somewhat diminished. Buying and selling houses is expensive and there are transcation costs with shares (albeit very much smaller).
Good luck.