Step 1: Start out with a 500 by 500px blank document and use the horizontal type tool to create a letter.  In this case, I've used the 'Ravie' font at size 150.  Don't worry if you don't have this particular typeface - just select something else with plenty of fat curves in it (they'll show off the effect to its fullest potential).

Step 2: With the type layer selected, click on Layer > Layer Style > Blending Options in the menu and make your settings resemble those on the left.   The 'fill opacity' option will determine the overall transparency of the whole effect.  In this case, I've selected 80%, but if you want the plastic effect to be totally opaque, go for 100%. 

NB.  If an option isn't displayed in the examples to the left, just leave it at PS default.

Step 3: OK, we now need to select the dominant colour of the text.  Go to the 'colour overlay' section, enable it, and choose the red colour and settings indicated on the right.  Repeat this for the 'drop shadow' subsection.  Note that the shadow colour is NOT black but a dark red.  Pure black tends to be a tad too strong and ruin the effect of semi-transparency.

Step 4: In a similar vein to the above step, go to the 'outer glow' section and fill in the settings as they are on the left.  This will create an almost imperceptible haze around the object - as if light were refracting through the dense plastic and out of the sides.

Step 5: Ok, this is where you'll wonder if you're reading the correct tutorial.  Enter the settings on the left into the 'inner shadow' section.  The result will resemble a cut-out of some variety - this will create the illusion of depth after step 7 has been completed. If you want your plastic text to appear deeper in the end, consider making this darker.  Don't overdo it though, or you'll muddy the colours.

Step 6: This is the last step before you'll see the results of your hard work.  Enter the 'inner glow' settings on the left.  This is another almost imperceptible tweak that will add a touch  of brightness to the underside arches of your lettering and create a more realistic sense of depth.

Step 7: Right - this is where it all happens!   Take care to replicate all the 'bevel & emboss' settings on the left fully or you'll end up with a substandard result.  You can edit the highlights and sense of thickness by adjusting the 'depth' and 'altitude' parameters accordingly.

Step 8: The plastic effect generated so far is pretty sweet, but still appears a tad too fuzzy.  Tighten up the highlights by going into the 'contour' subsection (not the 'gloss contour' section of 'bevel & emboss' - its the section below it) and replicate the contour on the left. You won't find it in the standard PS contours, but its simple enough to make your own anyway.

Step 9: This is an optional step, but adds a little something special in my opinion.  Make the text appear slightly mottled by entering the 'satin' details on the left.  The contour is a standard PS one known as 'ring'.    You can also try 'double ring' for a really intense effect.

Step 10: And that's it! As I mentioned in the introduction, the best thing about this technique is that you can copy the style across to almost any object. The little design on the left, for example, took a mere 10 seconds to create. If so inclined, you can also modify it slightly to give a 'jelly' look.  Just don't overdo it or you might start a new trend.  Have fun!  =)