I did an MBNA limit increase about a year ago and just called their number on the back of the card and waited for a representative and told them I wanted to speak to someone about a limit increase. They asked my about my income, graduation date, etc. and they got back to me in about 5 minutes. They also asked my what kind of limit I wanted. I went from $1500 to $2500. (But I only wanted a $1000 increase) I had the account since '98, so I don't know how much that helped. I was about $400 from the limit when I requested it.
They're pretty good about increasing me $500 every so often, but I make a note to call every 6-9 mos and ask for big increases. They'll pull a hard inquiry, but they've been very nice in helping me; currently my highest limit card.
I've found them to be very generous with increases. For a while they were doing it every 3 months, but on average I would say they increase about every 6 months. I've never asked for one, they've just given them. I use both of their cards pretty frequently.
