We switched children 1 & 2 to cups at 5 months by going "cold-turkey". Child 1 didn't drink much for a couple of days but wasn't fussed about it (he's remarkably laid back!) and then by about day 3 just got it and away he went. Child 2 definitely fussed (she is NOT laid-back!) and also didn't drink much for a couple of days but then got it and away we went with her.
(I should say that my HV was fully supportive of doing it this way and we ensured that they had plenty of milk and other liquids in their food for those few days.)
Children nos. 3&4 are now 7 months and we need to make the switch. We started on Wednesday and twin 2 got it straight away and sucked quite happily. She didn't take a huge amount, but was quite happy and able to suck and swallow. Twin 1 was less happy about it, but still made a few attempts to suck so we knew she could do it, although she had very little throughout the day. Yesterday they both drank a good amount at breakfast, albeit with ALOT of screaming from Twin 1. They then drank very little the rest of the day and were not very happy about the cups! They aren't bothered in between feeds, aren't showing any signs of being extra hungry or anything and still have plenty of energy. They are eating fine, just don't want to drink out of the cup. Today they have both screamed and arched their backs and refused to drink. I have managed to get some down them both and they had plenty mixed in with their cereal but it was only a small amount.
I know they are capable of drinking out of the cup - they just don't want to. Going back onto bottles and trying again in a few months isn't an option - they have teeth coming through and I'm not happy with them having a bottle once they have teeth. (This was part of the reason for doing the other 2 at 5 months as that was when they got their first teeth)
So how did you do it?
(apologies for the long post - I always like to read OPs with as much info as possible!)