Roundabouts are relatively new here and some drivers are still perplexed by them. That said, inexperience usually results in them getting around slower and sometimes yielding when they shouldn't (to vehicles looking to enter), so while it's annoying, it's usually not dangerous. On the whole, I like roundabouts a lot, both in the car and on the bike - even on roads with 50+ mph speed limits, the circles slow down to 20mph and are easily navigable.