In theory yes, it uses the maximum allowable bitrate at all times. In practise, well I challenge you to pick them out in a double blind test. Also just because the bits are there, doesn't mean the MP3 encoder finds a way to make use of them, they can go to waste (that's why you use VBR in the first place). As incog said, if you are that particular just go lossless and forget it. If you really can't swing the extra bitrate for lossless files, at least go with a better lossy format. MP3 is one of the least efficient out there. No surprise, it was a real pioneer and there's been lots of advancement since then. However you'll get better results at a given bitrate with something newer like OGG Vorbis, AAC, or WM-9.
The real answer for high bitrate stuff is just lossless though. As the name implies it is lossless, and not just in an acoustical sense. It is mathematically lossless and reconstructs the original PCM data bit for bit. You can prove it with a simple file diff utility (I did so on Head-Fi at one point, but I'm not sure some people were convinced).
It's not generally necessary to do lossless rips, even on really good gear it's rare you'll find the piece that you can tell the difference between 256k MP3 and lossless, however with disk space so cheap it provides an easy way to make sure that it is as good as it can be regardless of anything else.