A general question.
When you go to your "Lead Database" in Marketo what is the percent of your marketable leads?
I look at a number of things to determine how my database is doing. Usually I record the data quarterly but check it more often than that to keep an eye on things, especially after major events or lead generating activities.
I track the rate of my total DB and marketable DB on how many have a specific persona and how many are missing a persona so I can try to find other ways to trigger that information/make a campaign to gather the data I need to determine what persona people are.
I record industry, job level / function, location, sales territory, etc. so I can see over time how my database is growing and changing. It's helpful to see if one territory has more prospects than another or maybe one has a large number that are not marketable.
3. Data Completeness
I want to know how much standard information I'm missing - people with no phone number, country, job title, etc. so that I can determine if the leads we're pulling in over time are good quality with a lot of information, or if the campaigns I'm running are able to grab this data through things like progressive profiling.
I also have another section that looks at some basic data pieces - how many known duplicates do I have? How many unsubscribed? Bounced? Inactivity for the last 90 days?
We have a quite similar approach. If it is hard to define personas, you can use target accounts + target job titles (or job level + department/role). Also, we measure engagement and activity level within the target accounts and titles - to ensure we are interacting with the right audience. Plus every metric is looked upon dynamically, how it is changed over the time.