Sodium and Weight Gain?

Here's my own opinion, though it is based on some informed reading.
Sodium is not particularly good for you if you've got hypertension or other health issues of a similar nature.
If you don't have those issues, it's not such a big deal. (I no longer have high blood pressure, so I don't tend to worry about it.)
Sodium intake will make you retain water, so a couple of days of eating too much salt will be likely to shoot your weight up, but this is a temporary thing and should have minimal impact on your actual fat loss (which, really, is what you want).

So, if you weigh yourself too frequently, it's going to make your measurements bounce around a bit if you have a couple salty dogs the night before. Otherwise, I wouldn't worry about it.

And while there's some indication that truly excess salt will knock your kidneys around eventually, unless you're freebasing gherkins on a regular basis, just make sure you have plenty of water.

Too much sodium won't affect actual weight loss, nor will it cause your body to hold onto or gain fat. It might cause your body to retain water, and since water is pretty heavy, it may show up on the scale.
If you're worried about your sodium intake and water retention, just cut down on the salt. You don't have to lower your calories to lower your sodium. If you eat a lot of frozen or pre-packaged food, you might want to switch to eating more home-cooked and fresh foods. Also, drink lots of water. If your body is retaining water, drinking more water will help flush it out.