I used to do this journey on a regular basis and offer the following observations!
1. The train is VERY expensive (a mind boggling Day Return price of £31, unless you travel off peak) - the bus is MUCH cheaper, more frequent (every 10 mins or so, even running through the night), more comfortable and it even drops you off at various locations around Oxford and London - see
www.oxfordtube.com and
www.oxfordbus.co.uk/espress1 for details of the two companies that do this route. The only downside is the time it takes and the fact you will get stuck in traffic - average journey times are 1.5 to 2 hrs (the train is 1 hr)
2. The train is not bad, it goes at least every 30 mins (more in rush hour) although the actual trains are a bit dated and can get very packed as you approach London, but getting on at Oxford means you should always get a seat. Trains are now run by First Great Western (see
www.firstgreatwestern.co.uk) - they have just acquired the franchise from the previous operator, so things may get better??!!
3. The train drops you at Paddington, which is then a tube ride to anywhere else. Paddington is served by the utterly hopeless Circle Line - possibly the worst line on the Underground - however, on the plus side, the Bakerloo line also serves Paddington and this is a good service. So, check on where you want to get to in London.
4. Maybe live in between London and Oxford? Reading is OK (it won't win any awards for architecture, but it's a pleasant, if busy, biggish city and great for public transport) - otherwise there are some nice towns and villages strung out along the Thames Valley rail line (Maidenhead, Taplow, Windsor).
Good luck with the move and the jobs! Oxford is a great city and London is a lot of fun! Any more questions, let me know!