On my Media Centre setup I started with an MSI Digivox on /dev/dvb/adaptor0 and this worked well for quite a while, but the single tuner proved more and more limiting as time went on and my PVR started gathering dust.
As I wanted to add Freesat I got a "DM04" for £15 from eBay (£15 - but seriously don't bother - waited nine weeks for shipping and it's pants, gives up working after a while and requires service tvheadend stop; unplug usb; plug usb; service tvheadend start at least once a day - annoyingly if you leave the channel you want to record playing it WILL work, if you don't there's a 50:50 chance...) - anyway when I got this it appeared on /dev/dvb/adaptor1 and happily stayed there through reboots.
This tuner being so rubbish prompted me to get a a Kworld UB499-2T which (once you turned "Disable PMT monitoring" on) works wonderfully on /dev/dvb/adaptor2 and /dev/dvb/adaptor3 ....
So in summary...
/dev/dvb/adaptor0 = Twinhan VP7045/46 USB DVB-T (MSI Digivox) - USB Bus 2 Port 3 (Renamed Freeview - MSI Digivox)
/dev/dvb/adaptor1 = Freesat DM04_LME2510C_DVB-S RS2000 (DM04) - USB Bus 2 Port 2 (Renamed Freesat - DM04)
/dev/dvb/adaptor2 = Kworld UB499-2T T09(IT9137)_1 (KWorld UB499-2T Tuner 1) - USB Bus 2 Port 1 (Renamed Freeview - Kworld 1)
/dev/dvb/adaptor3 = Kworld UB499-2T T09(IT9137)_1 (KWorld UB499-2T Tuner 2) - USB Bus 2 Port 1 (Renamed Freeview - Kworld 2)
Then I rebooted the machine and for some reason Ubuntu decided to put them on the following adaptors
/dev/dvb/adaptor0 = Kworld UB499-2T T09(IT9137)_1 (KWorld UB499-2T Tuner 1) - USB Bus 2 Port 1
/dev/dvb/adaptor1 = Kworld UB499-2T T09(IT9137)_1 (KWorld UB499-2T Tuner 2) - USB Bus 2 Port 1
/dev/dvb/adaptor2 = Twinhan VP7045/46 USB DVB-T (MSI Digivox) - USB Bus 2 Port 3
/dev/dvb/adaptor3 = Freesat DM04_LME2510C_DVB-S RS2000 (DM04) - USB Bus 2 Port 2
Is there any way to either a) force Ubuntu to always leave them on the same port (/etc/modules has the modules entered in the order I added the cards - i.e. the tope one), or ensure TVHeadend copes with Ubuntu doing daft things.
Don't particularly fancy getting 13 tuners listed when I eventually add a DVB-S2 tuner (already got 8 when only (3 physical) 4 (logical) tuners exist)!
Fortunately copying the multiplexes also copied the enabled channels which saved me a while, was a bit surpised when East Midlands Today suddenly started bursting out the TV!