Tracking/Reporting Record Hits.

I am serving ad-units. In each ad-unit I show somewhere between 3 and 10 article headline. I track the headline impressions to get an idea of the headline click through rate. I save the output from the stats process in another table. I am currently evaluating the stats every hour, and then truncating the table every night at midnight. The problem is that I get lots of impressions and the database gets bogged down evaluating the data such as...
SELECT COUNT FROM articleimpressions WHERE articleid = x

But the issue isn't the reporting of the data...so much as it's the capture. I had to add caching on the ad-server because the database couldn't handle the number of inserts.

I thought about parsing the web server log files the next day, but the file sizes seem to be too large, and I can't process them all in one day. (At least not on the hardware that I am using.)

I've thought about splitting log files by hour, but was wondering if there may be a more "native" solution within SQL Server? Maybe a trigger, and/or multi-threaded SP that fires and forgets an insert statement to a linked server. But performance is the key here.

Thoughts?