I have had mostly good experiences with hotel-derived miles posting with no additional intervention from me. I send almost all my hotel credits to BA EC, and they tend to post within 2-3 weeks. The only tricky part is with overseas hotels (I travel mostly in emerging-market countries)--the desk staff are often unfamiliar with the whole concept of earning miles for stays, so you have to keep on top of them.

I have only tried to earn miles from a car rental once (also overseas, with National) and despite paying EUR 2 for the privilege and following up with National afterwards, I have yet to see any miles in my account. At 50 miles a day for a car rental, it doesn't seem worth the hassle to even bother with this.