Zwiebelfisch in Spiegel Online (Bastian Sick; thanks to Josip Korbar of the pt mailing list for reminding me) writes about how English words are handled in German text.
How often I wonder something like downgeloadet? gedownloadet? downgeloaded? I recall the alternative gesaugt, but I have a feeling there must be a better one. Yes, heruntergeladen.
In principle, says the article, treat the words just as the English language treats words from the German: bratwurst, bratwursts, abseil, abseiling (but I write Land, Länder in English texts and can’t bring myself to write Amtsgerichts – or bratwursts for that matter).
Sometimes you can avoid the problem by using a German word: not forgewardet or geforwardet, but weitergeleitet; not gevotet, but abgestimmt; not upgedated, but aktualisiert; not gebackupt, but gesichert.
But sometimes the English word is simpler than the German: gestylt, gepixelt, gescannt, simsen (to send SMSs), chatten.