If your Magento product imports and exports certainly aren’t as speedy as they used to be, it could be that the database table is just filling up with old records. There are a few to look at.

dataflow_batch_import
dataflow_batch_export
log_url
log_url_info
log_visitor
log_visitor_info

The dataflow records can be quickly emptied in mysql or your database:

truncate table dataflow_batch_import;
truncate table dataflow_batch_export;

Just run the query about to remove the old data.  This will not harm your site.  Just make sure that you are not uploading / importing / exporting products at the time. 

For your logs – I would suggest you correctly set up log cleaning, this relies on the Magento Cron being correctly set up.
1) Log into your Magento admin and go to System > Configuration
2) Scroll down to Advanced > System
3) Select Log Cleaning
4) Change “save log, days” to a sensible figure, we use 30.
5) Enable log cleaning