I am with Boothe on this one. 44.1KHz is audio standard and has been for ages.
There are some advantages to using 48Khz (but mainly to 88/96 and 176/192) in production and recording environments. The higher the frequency the better when manipulating sounds.
But, unless you are releasing a video, ALL audio gets bounced back to 16-bit/44.1KHz for general public consumption. Why? Because it will play on any piece of equipment out there. This is CD-quality sound and higher quality serves no purpose. Especially in DJ environments. If you, indeed for any reason, acquire 48KHz MP3 from some source, the best bet is to do a ONE-TIME conversion, using high quality hard-/software with max. quality (usually slow) settings. After that, only use the 44.1KHz version of your file. Better still would be to rip from the original source (a DVD for example) straight into WAV or some other lossless format like FLAC. Keep that as your base, untouched file in archive and use it to do any audio preparation you like to do (whether it be manipulating BPM in Ableton, volume/gain correction in any of the available programs or running your tracks through Platinum Notes). Only when you are done with manipulation should you do the final conversion to 44.1KHz MP3.
In my very humble opinion, the MP3 320 sound quality is great for DJ-purposes as it’s just about impossible to tell the difference in the typical DJ environment and it lets you store a lot of tracks on small devices like USB-sticks. The other advantage being that MP3 is accepted on every DJ software platform and most recent DJ gear, which is not always true for lossless formats like FLAC and AIFF for example. WAV is not a good DJ format due to it’s lack of proper tagging options. There is however no added value to having 48KHz sample rate, while it does put extra demands on hardware/software.