Normally Magento would push a cron error via email to the email address you have entered in the Admin for this. Optionally errors would be logged to exception.log in the var/log directory.

[EDIT]

You can monitor your cronjob activity with Aoe_Scheduler. That might also give you some more insight into whats going on.

[END EDIT]

I usually turn of logging since it's not very useful and does a lot of queries per page view. You can turn them off via a modules config.xml by adding 

&lt;frontend&gt;
        &lt;events&gt;
            &lt;controller_action_predispatch&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/controller_action_predispatch&gt;
            &lt;controller_action_postdispatch&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/controller_action_postdispatch&gt;
            &lt;customer_login&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/customer_login&gt;
            &lt;customer_logout&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/customer_logout&gt;
            &lt;sales_quote_save_after&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/sales_quote_save_after&gt;
            &lt;checkout_quote_destroy&gt;
                &lt;observers&gt;&lt;log&gt;&lt;type&gt;disabled&lt;/type&gt;&lt;/log&gt;&lt;/observers&gt;
            &lt;/checkout_quote_destroy&gt;
        &lt;/events&gt;
    &lt;/frontend&gt;


Or just download the module I've build for this.
https://github.com/sandermangel/sama_disablelog

Do Cron_schedule table collects log cleaning status too?
I've used the "Reports and Graphs" section of Quicken in a very basic capacity to see where my money has been going -- "Income / Expenses" and "Spending by Category" mostly -- and I've been trying to branch out and try the other reports/graphs to get a better idea of my finances.

Here's what I'd like to do:  See a simple graph that shows how much of my money went to Savings each month.

The closest I've found is the "Net Worth" chart, where the amount it goes up (or down) is the amount I've saved (or overspent).  I'd like one that shows (Total Income - Total Expenses) over time.  I've also tried the "Income/Expense" Graph, but that shows separate bars for income and expense, and I want to show a single bar (or a line graph would be nice too).
