For a blog that only receives occasional small amounts you probably shouldn't worry too much about it. However, if you plan to scale up, here are some things to consider:
One issue with using the same address for all transactions is that people can see the total amount received by that address and know how many bitcoins you have. If the total is large enough, this might make you a target for attack, especially if you publish personal information along with the bitcoin address.
Another potential issue is that people can see who else is donating to you. They only see the bitcoin addresses used, but this might be enough to draw some conclusions about who they are.
Best practice is to use new addresses for each donation. This way there is no link among the transactions except in your wallet, which is only accessible by you.
If you plan to keep bitcoins (instead of just receiving them and cashing them in), you should look into creating an offline wallet. You could generate a new address for each web page view, and then transfer funds from each of the addresses that received a donation to a different pre-computed offline wallet address.