The theory has it that in the US people tend to voice intervocalic "T" like in writer sounding more or less like rider. My question is - how do Americans perceive voiceless pronunciation? (Not only in the word I used as an example) Does it sound how? Careful? British? Snobby? Regional?
Of course, asking how it sounds from the worldwide English community, you are likely to receive a few different answers, so anything here will be highly subjective.
Coming from an Australian point of view, the use of depends on the richness of the accent. Certain areas of Sydney, for example, have stronger and more regional-sounding accents, which generally sound very casual and laid-back. If ever you listen to really rich Aussie accent, you would definitely NOT consider it 'careful', 'British' or 'snobbish'. If anything, it's lazy and my parents certainly called me up on it when I spoke that way as a child.
Examples of lazy Australian pronunciation include 'rider' rather than 'writer' though with a soft 'd' sound - almost like 'rye-er', 'twenny' rather than 'twenty', dropping the 't' from words such as 'want', 'track-der' rather than 'tractor'...
In many ways, it's very similar to what you would find in American English pronunciation.
My parents regarded speaking in that way as lazy (they were both British-born) and, to be honest, it does sound lazy and a bit uncouth, especially from younger speakers. Others, however, think it's hilarious. It also depends a lot on the tone of the voice, as many Australian speaks can sound very nasal. So that side of things is very subjective.
I used to work as a captioner (subtitler with sound effects included for the hearing impaired) and many words tripped me up when listening to American English speakers. The hardest to decipher was when an American was saying 'God' or 'guard'. I couldn't tell the difference at all! Had to rely on context alone. Not as easy as it sounds!