Uhm, in short… USB is crap crap crap. Sell your midisport to some poor soul who doesn’t care, and buy a better but older interfface with the money, then take your girlfriend to dinner with the change 
USB is great for the consumer and the mildly computer illiterate, because most of the time you can just plug it in and it goes. So it’s great for your Mum to use if she wants to install a printer, or for your young children to plug in a camera and automatically download photos…etc…
Because of this, and because we live in a society where “majority rules, even though the majority are fools”, USB has become a standard. Once something gets that popular, humans being the sheep that we are, do not ask questions. It’s a subconcsious “well it’s what everyone else uses, it must be OK”
Well I for one don’t buy it. (pun intended)
It’s buggy and slow and most importantly for high-end audio stuff, it interrupts your CPU. It causes skips in audio, jumps and lags in MIDI, screen redraw problems… Basically anything that uses the CPU gets paused when USB feels like it.
IMHO, USB took off purely as a result of the MS/Intel alliance putting heaps of cash behind the protocol and flooding the market in order to compete with firewire for market share. The fact is, most computers users are PC users, not mac. When all the PC’s start to have USB interfaces built in, and you can no longer buy an intel chipset without the interface, the interface becomes a pseudo standard. It’s certainly not the first time that MS have twisted the industry standards in order to have things their own way. This is not some anti wintel argument, heck I’m a wintel techo among other things, and I really like a lot of MS’s features… But I’m just calling it how I see it.
I’ve found that when the CPU is a bit maxxed out (you know, too many VSTi running, 99% CPU… We’ve all been there ) serial MIDI interfaces can sometimes get a bit laggy and drift. Sometimes. Cheapo soundcard onboard MIDI is not really designed for heavy/pro use, most SB cards will easily crap themselves if they have a long enough sysex string sent or recieved (especially recieved). Personally I recommend Parallel MIDI interfaces, and they’re really bloody cheap now because the majority don’t want them cause they’re old (“I want new toys” syndrome). (Parallel MIDI interfaces that were $800 on ebay last year or two are now $100)
Best, but more expensive, is a MIDI interface on a PCI card (I’ve never seen a PCI card with MIDI but no audio…anyone else?)…
I haven’t had the opportunity to test any firewire midi interfaces so I shouldn’t comment, but I will go out on a limb and say that they’re probably very good too.
It is imperative that you turn off stupid ACPI and IRQ steering (grrrr!!! another wintel strongarm tactic) and manually set IRQ’s for the PCI cards in your PC’s BIOS, and disable the USB interface in the BIOS (Just disabling in windows will not help, the interface is still active, just being ignored by the drivers that way). If you don’t do these things then don’t expect good performance in any CPU intensive area, no matter what your choice of peripherals and software. Which PCI card is in which slot also has an effect on performance, as two slots are shared, and the cards are accessed in slow order… So your audio interfaces should be in the first PCI slots where available.
Your mobo has wireless lan in it, I would definitely turn that off!!
PS there’s a little info on this from EM mag and the man currently responsible for the MIDI standard … Just in case you don’t think I’m ‘pro’ enough to make thse statements http://emusician.com/mag/emusic_letters_5/
More backup for my opinion from SOS… read the recap bit http://www.soundonsound.com/sos/Oct02/articles/pcmusician1002.asp
A bit of searching on google will find (under other names) me making this same tirade about 5 years ago.
My apologies to anyone in the industry but… I TOLD YOU SO!! 
I should add that although I personally can’t stand the fact that USB even exists, let alone is still being used… It does have it’s advantages (see above), so it’s really a matter of what is most important to you. If you’ve got a dual xeon with 16g of ram you probably won’t max it out too often and these interruptions would not rate as such an issue. And you should donate your PC to me ;D
